var isPalindrome = function(head) {
let left = head;
function traverse(right) {
if (right == null) return true;
let res = traverse(right.next);
res = res && (right.val === left.val);
left = left.next;
return res;
}
return traverse(head);
};
3.反转链表
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var reverseList = function(head) {
if (head == null || head.next == null) return head;
let last = reverseList(head.next);
head.next.next = head;
head.next = null;
return last;
};
4. 合并K个升序链表(困难)
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode[]} lists
* @return {ListNode}
*/
var mergeKLists = function(lists) {
if (lists.length === 0) return null;
return mergeArr(lists);
};
function mergeArr(lists) {
if (lists.length <= 1) return lists[0];
let index = Math.floor(lists.length / 2);
const left = mergeArr(lists.slice(0, index))
const right = mergeArr(lists.slice(index));
return merge(left, right);
}
function merge(l1, l2) {
if (l1 == null && l2 == null) return null;
if (l1 != null && l2 == null) return l1;
if (l1 == null && l2 != null) return l2;
let newHead = null, head = null;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
if (!head) {
newHead = l1;
head = l1;
} else {
newHead.next = l1;
newHead = newHead.next;
}
l1 = l1.next;
} else {
if (!head) {
newHead = l2;
head = l2;
} else {
newHead.next = l2;
newHead = newHead.next;
}
l2 = l2.next;
}
}
newHead.next = l1 ? l1 : l2;
return head;
}
5. K 个一组翻转链表(困难)
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @param {number} k
* @return {ListNode}
*/
var reverseKGroup = function(head, k) {
let a = head, b = head;
for (let i = 0; i < k; i++) {
if (b == null) return head;
b = b.next;
}
const newHead = reverse(a, b);
a.next = reverseKGroup(b, k);
return newHead;
};
function reverse(a, b) {
let prev = null, cur = a, nxt = a;
while (cur != b) {
nxt = cur.next;
cur.next = prev;
prev = cur;
cur = nxt;
}
return prev;
}
5. 环形链表(简单)
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {boolean}
*/
var hasCycle = function(head) {
if (head == null || head.next == null) return false;
let slower = head, faster = head;
while (faster != null && faster.next != null) {
slower = slower.next;
faster = faster.next.next;
if (slower === faster) return true;
}
return false;
};
6. 排序链表(中等)
/**
* Definition for singly-linked list.
* function ListNode(val) {
* this.val = val;
* this.next = null;
* }
*/
/**
* @param {ListNode} head
* @return {ListNode}
*/
var sortList = function(head) {
if (head == null) return null;
let newHead = head;
return mergeSort(head);
};
function mergeSort(head) {
if (head.next != null) {
let slower = getCenter(head);
let nxt = slower.next;
slower.next = null;
console.log(head, slower, nxt);
const left = mergeSort(head);
const right = mergeSort(nxt);
head = merge(left, right);
}
return head;
}
function merge(left, right) {
let newHead = null, head = null;
while (left != null && right != null) {
if (left.val < right.val) {
if (!head) {
newHead = left;
head = left;
} else {
newHead.next = left;
newHead = newHead.next;
}
left = left.next;
} else {
if (!head) {
newHead = right;
head = right;
} else {
newHead.next = right;
newHead = newHead.next;
}
right = right.next;
}
}
newHead.next = left ? left : right;
return head;
}
function getCenter(head) {
let slower = head, faster = head.next;
while (faster != null && faster.next != null) {
slower = slower.next;
faster = faster.next.next;
}
return slower;
}
/**
* @param {string} s
* @return {string}
*/
var longestPalindrome = function(s) {
if (s.length === 1) return s;
let maxRes = 0, maxStr = '';
for (let i = 0; i < s.length; i++) {
let str1 = palindrome(s, i, i);
let str2 = palindrome(s, i, i + 1);
if (str1.length > maxRes) {
maxStr = str1;
maxRes = str1.length;
}
if (str2.length > maxRes) {
maxStr = str2;
maxRes = str2.length;
}
}
return maxStr;
};
function palindrome(s, l, r) {
while (l >= 0 && r < s.length && s[l] === s[r]) {
l--;
r++;
}
return s.slice(l + 1, r);
}
9. 最长公共前缀(简单)
/**
* @param {string[]} strs
* @return {string}
*/
var longestCommonPrefix = function(strs) {
if (strs.length === 0) return "";
let first = strs[0];
if (first === "") return "";
let minLen = Number.MAX_SAFE_INTEGER;
for (let i = 1; i < strs.length; i++) {
const len = twoStrLongestCommonPrefix(first, strs[i]);
minLen = Math.min(len, minLen);
}
return first.slice(0, minLen);
};
function twoStrLongestCommonPrefix (s, t) {
let i = 0, j = 0;
let cnt = 0;
while (i < s.length && j < t.length) {
console.log(s[i], t[j], cnt)
if (s[i] === t[j]) {
cnt++;
} else {
return cnt;
}
i++;
j++;
}
return cnt;
}
10. 无重复字符的最长子串(中等))
/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function(s) {
let window = {};
let left = 0, right = 0;
let maxLen = 0, maxStr = '';
while (right < s.length) {
let c = s[right];
right++;
if (window[c]) window[c]++;
else window[c] = 1
while (window[c] > 1) {
let d = s[left];
left++;
window[d]--;
}
if (maxLen < right - left) {
maxLen = right - left;
}
}
return maxLen;
};
11. 最小覆盖子串(困难)
/**
* @param {string} s
* @param {string} t
* @return {string}
*/
var minWindow = function(s, t) {
let need = {}, window = {};
for (let c of t) {
if (!need[c]) need[c] = 1;
else need[c]++;
}
let left = 0, right = 0;
let valid = 0, len = Object.keys(need).length;
let minLen = s.length + 1, minStr = '';
while (right < s.length) {
const d = s[right];
right++;
if (!window[d]) window[d] = 1;
else window[d]++;
if (need[d] && need[d] === window[d]) {
valid++;
}
console.log('left - right', left, right);
while (valid === len) {
if (right - left < minLen) {
minLen = right - left;
minStr = s.slice(left, right);
}
console.lo
let c = s[left];
left++;
window[c]--;
if (need[c] && window[c] < need[c]) {
valid--;
}
}
}
return minStr;
};
12. 俄罗斯套娃信封问题(困难)
/**
* @param {number[][]} envelopes
* @return {number}
*/
var maxEnvelopes = function(envelopes) {
if (envelopes.length === 1) return 1;
envelopes.sort((a, b) => {
if (a[0] !== b[0]) return a[0] - b[0];
else return b[1] - a[1];
});
let LISArr = [];
for (let [key, value] of envelopes) {
LISArr.push(value);
}
console.log( LISArr);
return LIS(LISArr);
};
function LIS(arr) {
let dp = [];
let maxAns = 0;
for (let i = 0; i < arr.length; i++) {
dp[i] = 1;
}
for (let i = 1; i < arr.length; i++) {
for (let j = i; j >= 0; j--) {
if (arr[i] > arr[j]) {
dp[i] = Math.max(dp[i], dp[j] + 1)
}
maxAns = Math.max(maxAns, dp[i]);
}
}
return maxAns;
}
13. 最长连续递增序列(简单)
/**
* @param {number[]} nums
* @return {number}
*/
var findLengthOfLCIS = function(nums) {
if (nums.length === 0) return 0;
const n = nums.length;
let left = 0, right = 1;
let globalMaxLen = 1, maxLen = 1;
while (right < n) {
if (nums[right] > nums[left]) maxLen++;
else {
maxLen = 1;
}
left++;
right++;
globalMaxLen = Math.max(globalMaxLen, maxLen);
}
return globalMaxLen;
};
14. 最长连续序列(困难)
/**
* @param {number[]} nums
* @return {number}
*/
var longestConsecutive = function(nums) {
if (nums.length === 0) return 0;
const set = new Set(nums);
const n = nums.length;
let globalLongest = 1;
for (let i = 0; i < n; i++) {
if (!set.has(nums[i] - 1)) {
let longest = 1;
let currentNum = nums[i];
while (set.has(currentNum + 1)) {
currentNum += 1;
longest++;
}
globalLongest = Math.max(globalLongest, longest);
}
}
return globalLongest;
};
15. 盛最多水的容器(中等)
/**
* @param {number[]} height
* @return {number}
*/
var maxArea = function(height) {
let n = height.length;
let left = 0, right = n - 1;
let maxOpacity = 0;
while (left < right) {
let res = Math.min(height[left], height[right]) * (right - left);
maxOpacity = Math.max(maxOpacity, res);
if (height[left] < height[right]) left++
else right--;
}
return maxOpacity;
};
16. 寻找两个正序数组的中位数(困难)
/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number}
*/
var findMedianSortedArrays = function(nums1, nums2) {
let m = nums1.length, n = nums2.length;
let i = 0, j = 0;
let newArr = [];
while (i < m && j < n) {
if (nums1[i] < nums2[j]) {
newArr.push(nums1[i++]);
} else {
newArr.push(nums2[j++]);
}
}
newArr = newArr.concat(i < m ? nums1.slice(i) : nums2.slice(j));
const len = newArr.length;
console.log(newArr)
if (len % 2 === 0) {
return (newArr[len / 2] + newArr[len / 2 - 1]) / 2;
} else {
return newArr[Math.floor(len / 2)];
}
};
17. 删除有序数组中的重复项(简单)
/**
* @param {number[]} nums
* @return {number}
*/
var removeDuplicates = function(nums) {
if (nums.length <= 1) return nums.length;
let lo = 0, hi = 0;
while (hi < nums.length) {
while (nums[lo] === nums[hi] && hi < nums.length) hi++;
if (nums[lo] !== nums[hi] && hi < nums.length) {
lo++;
nums[lo] = nums[hi];
}
hi++;
}
return lo + 1;
};
18. 岛屿的最大面积(中等)
/**
* @param {number[][]} grid
* @return {number}
*/
let maxX, maxY;let visited;let globalMaxArea;
var maxAreaOfIsland = function(grid) {
visited = new Set();
maxX = grid.length;
maxY = grid[0].length;
globalMaxArea = 0;
for (let i = 0; i < maxX; i++) {
for (let j = 0; j < maxY; j++) {
if (grid[i][j] === 1) {
visited.add(`(${i}, ${j})`);
globalMaxArea = Math.max(globalMaxArea, dfs(grid, i, j));
}
visited.clear();
}
}
return globalMaxArea;
};
function dfs(grid, x, y) {
let res = 1;
for (let i = -1; i <= 1; i++) {
for (let j = -1; j <= 1; j++) {
if (Math.abs(i) === Math.abs(j)) continue;
const newX = x + i;
const newY = y + j;
if (newX >= maxX || newX < 0 || newY >= maxY || newY < 0) continue;
if (visited.has(`(${newX}, ${newY})`)) continue;
visited.add(`(${newX}, ${newY})`);
const areaCnt = grid[newX][newY]
if (areaCnt === 1) {
const cnt = dfs(grid, newX, newY);
res += cnt;
}
}
}
return res;
}
19. 和为K的子数组(中等)
/**
* @param {number[]} nums
* @param {number} k
* @return {number}
*/
var subarraySum = function(nums, k) {
let cnt = 0;
let sum0_i = 0, sum0_j = 0;
let map = new Map();
map.set(0, 1);
for (let i = 0; i <= nums.length; i++) {
sum0_i += nums[i];
sum0_j = sum0_i - k;
console.log('map', sum0_j, map.get(sum0_j))
if (map.has(sum0_j)) {
cnt += map.get(sum0_j);
}
let sumCnt = map.get(sum0_i) || 0;
map.set(sum0_i, sumCnt + 1);
}
return cnt;
};
nSum问题【哈希表】【系列】
1. 两数之和(简单)
/**
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var twoSum = function(nums, target) {
let map2 = new Map();
for (let i = 0; i < nums.length; i++) {
map2.set(nums[i], i);
}
for (let i = 0; i < nums.length; i++) {
if (map2.has(target - nums[i]) && map2.get(target - nums[i]) !== i) return [i, map2.get(target - nums[i])]
}
};
2. 接雨水(困难)
/**
* @param {number[]} height
* @return {number}
*/
var trap = function(height) {
let l_max = [], r_max = [];
let len = height.length;
let maxCapacity = 0;
for (let i = 0; i < len; i++) {
l_max[i] = height[i];
r_max[i] = height[i];
}
for (let i = 1; i < len; i++) {
l_max[i] = Math.max(l_max[i - 1], height[i]);
}
for (let j = len - 2; j >= 0; j--) {
r_max[j] = Math.max(r_max[j + 1], height[j]);
}
for (let i = 0; i < len; i++) {
maxCapacity += Math.min(l_max[i], r_max[i]) - height[i];
}
return maxCapacity;
};
跳跃游戏【贪心算法】【系列】
1. 跳跃游戏(中等)
/**
* @param {number[]} nums
* @return {boolean}
*/
var canJump = function(nums) {
let faster = 0;
for (let i = 0; i < nums.length - 1; i++) {
faster = Math.max(faster, i + nums[i]);
if (faster <= i) return false;
}
return faster >= nums.length - 1;
};
【二叉树】【系列】
1. 二叉树的最近公共祖先(简单)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {TreeNode} p
* @param {TreeNode} q
* @return {TreeNode}
*/
let visited;let parent;
var lowestCommonAncestor = function(root, p, q) {
visited = new Set();
parent = new Map();
dfs(root);
while (p != null) {
visited.add(p.val);
p = parent.get(p.val);
}
while (q != null) {
if (visited.has(q.val)) {
return q;
}
q = parent.get(q.val);
}
return null;
};
function dfs(root) {
if (root.left != null) {
parent.set(root.left.val, root);
dfs(root.left);
}
if (root.right != null) {
parent.set(root.right.val, root);
dfs(root.right);
}
}
2. 二叉搜索树中的搜索(简单)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {number} val
* @return {TreeNode}
*/
var searchBST = function(root, val) {
if (root == null) return null;
if (root.val === val) return root;
if (root.val > val) {
return searchBST(root.left, val);
} else if (root.val < val) {
return searchBST(root.right, val);
}
};
3. 删除二叉搜索树中的节点(中等)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @param {number} key
* @return {TreeNode}
*/
var deleteNode = function(root, key) {
if (root == null) return null;
if (root.val === key) {
if (root.left == null && root.right == null) return null;
if (root.left == null) return root.right;
if (root.right == null) return root.left;
if (root.left != null && root.right != null) {
let target = getMinTreeMaxNode(root.left);
root.val = target.val;
root.left = deleteNode(root.left, target.val);
}
}
if (root.val < key) {
root.right = deleteNode(root.right, key);
} else if (root.val > key) {
root.left = deleteNode(root.left, key);
}
return root;
};
function getMinTreeMaxNode(root) {
if (root.right == null) return root;
return getMinTreeMaxNode(root.right);
}
4. 完全二叉树的节点个数(中等)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number}
*/
var countNodes = function(root) {
if (root == null) return 0;
let l = root, r = root;
let lh = 0, rh = 0;
while (l != null) {
l = l.left;
lh++;
}
while (r != null) {
r = r.right;
rh++;
}
if (lh === rh) {
return Math.pow(2, lh) - 1;
}
return 1 + countNodes(root.left) + countNodes(root.right);
};
5. 二叉树的锯齿形层序遍历(中等)
/**
* Definition for a binary tree node.
* function TreeNode(val) {
* this.val = val;
* this.left = this.right = null;
* }
*/
/**
* @param {TreeNode} root
* @return {number[][]}
*/
let res;
var zigzagLevelOrder = function(root) {
if (root == null) return [];
res = [];
BFS(root, true);
return res;
};
function BFS(root, inOrder) {
let arr = [];
let resItem = [];
let node;
let stack1 = new Stack();
let stack2 = new Stack();
// 判断交换时机
let flag;
stack1.push(root);
res.push([root.val]);
inOrder = !inOrder;
while (!stack1.isEmpty() || !stack2.isEmpty()) {
if (stack1.isEmpty()) {
flag = 'stack1';
} else if (stack2.isEmpty()) {
flag = 'stack2';
}
// 决定取那个栈里面的元素
if (flag === 'stack2' && !stack1.isEmpty()) node = stack1.pop();
else if (flag === 'stack1' && !stack2.isEmpty()) node = stack2.pop();
if (inOrder) {
if (node.left) {
if (flag === 'stack1') {
stack1.push(node.left);
} else {
stack2.push(node.left);
}
resItem.push(node.left.val);
}
if (node.right) {
if (flag === 'stack1') {
stack1.push(node.right);
} else {
stack2.push(node.right);
}
resItem.push(node.right.val);
}
} else {
if (node.right) {
if (flag === 'stack1') {
stack1.push(node.right);
} else {
stack2.push(node.right);
}
resItem.push(node.right.val);
}
if (node.left) {
if (flag === 'stack1') {
stack1.push(node.left);
} else {
stack2.push(node.left);
}
resItem.push(node.left.val);
}
}
// 判断下次翻转的时机
if ((flag === 'stack2' && stack1.isEmpty()) || (flag === 'stack1' && stack2.isEmpty())) {
inOrder = !inOrder;
// 需要翻转了,就加一轮值
if (resItem.length > 0) {
res.push(resItem);
}
resItem = [];
}
}
}
class Stack {
constructor() {
this.count = 0;
this.items = [];
}
push(element) {
this.items[this.count] = element;
this.count++;
}
pop() {
if (this.isEmpty()) return undefined;
const element = this.items[this.count - 1];
delete this.items[this.count - 1];
this.count--;
return element;
}
size() {
return this.count;
}
isEmpty() {
return this.size() === 0;
}
}
【排序算法】【系列】
1. 用最少数量的箭引爆气球(中等)
/**
* @param {number[][]} points
* @return {number}
*/
var findMinArrowShots = function(points) {
if (points.length === 0) return 0;
points.sort((a, b) => a[1] - b[1]);
let cnt = 1;
let resArr = [points[0]];
let curr, last;
for (let i = 1; i < points.length; i++) {
curr = points[i];
last = resArr[resArr.length - 1];
if (curr[0] > last[1]) {
resArr.push(curr);
cnt++;
}
}
return cnt;
};
2. 合并区间(中等)
/**
* @param {number[][]} intervals
* @return {number[][]}
*/
var merge = function(intervals) {
if (intervals.length === 0) return [];
intervals.sort((a, b) => a[0] - b[0]);
let mergeArr = [intervals[0]];
let last, curr;
for (let j = 1; j < intervals.length; j++) {
last = mergeArr[mergeArr.length - 1];
curr = intervals[j];
if (last[1] >= curr[0]) {
last[1] = Math.max(curr[1], last[1]);
} else {
mergeArr.push(curr);
}
}
return mergeArr;
};
【 二分查找 】
1. 寻找两个正序数组的中位数(困难)
/**
* @param {number[]} nums1
* @param {number[]} nums2
* @return {number}
*/
var findMedianSortedArrays = function(nums1, nums2) {
let m = nums1.length, n = nums2.length;
let i = 0, j = 0;
let newArr = [];
while (i < m && j < n) {
if (nums1[i] < nums2[j]) {
newArr.push(nums1[i++]);
} else {
newArr.push(nums2[j++]);
}
}
newArr = newArr.concat(i < m ? nums1.slice(i) : nums2.slice(j));
const len = newArr.length;
console.log(newArr)
if (len % 2 === 0) {
return (newArr[len / 2] + newArr[len / 2 - 1]) / 2;
} else {
return newArr[Math.floor(len / 2)];
}
};
2. 判断子序列(简单)
/**
* @param {string} s
* @param {string} t
* @return {boolean}
*/
var isSubsequence = function(s, t) {
let hash = {};
for (let i = 0; i < t.length; i++) {
if (!hash[t[i]]) hash[t[i]] = [];
hash[t[i]].push(i);
}
let lastMaxIndex = 0;
for (let i = 0; i < s.length; i++) {
if (hash[s[i]]) {
const index = binarySearch(hash[s[i]], lastMaxIndex);
console.log('index', index, hash[s[i]]);
if (index === -1) return false;
lastMaxIndex = hash[s[i]][index] + 1;
} else return false;
}
return true;
};
function binarySearch(array, targetIndex) {
let left = 0, right = array.length;
while (left < right) {
let mid = left + Math.floor((right - left) / 2);
if (array[mid] >= targetIndex) {
right = mid;
} else if (array[mid] < targetIndex) {
left = mid + 1;
}
}
if (left >= array.length || array[left] < targetIndex) return -1;
return left;
}
3. 在排序数组中查找元素的第一个和最后一个位置(中等)
/**
* @param {number[]} nums
* @param {number} target
* @return {number[]}
*/
var searchRange = function(nums, target) {
const left = leftBound(nums, target);
const right = rightBound(nums, target);
return [left, right];
};
function leftBound(nums, target) {
let left = 0;
let right = nums.length - 1;
while (left <= right) {
let mid = Math.floor(left + (right - left) / 2);
if (nums[mid] === target) {
right = mid - 1;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid - 1;
}
}
if (left >= nums.length || nums[left] !== target) {
return -1;
}
return left;
}
function rightBound(nums, target) {
let left = 0;
let right = nums.length - 1;
while (left <= right) {
let mid = Math.floor(left + (right - left) / 2);
if (nums[mid] === target) {
left = mid + 1;
} else if (nums[mid] < target) {
left = mid + 1;
} else if (nums[mid] > target) {
right = mid - 1;
}
}
if (right < 0 || nums[right] !== target) {
return -1;
}
return right;
}