原题链接在这里：https://leetcode.com/problems/minimum-number-of-steps-to-make-two-strings-anagram/

题目：

You are given two strings of the same length s and t. In one step you can choose any character of t and replace it with another character.

Return the minimum number of steps to make t an anagram of s.

An Anagram of a string is a string that contains the same characters with a different (or the same) ordering.

Example 1:

Input: s = "bab", t = "aba"
Output: 1
Explanation: Replace the first 'a' in t with b, t = "bba" which is anagram of s.

Example 2:

Input: s = "leetcode", t = "practice"
Output: 5
Explanation: Replace 'p', 'r', 'a', 'i' and 'c' from t with proper characters to make t anagram of s.

Example 3:

Input: s = "anagram", t = "mangaar"
Output: 0
Explanation: "anagram" and "mangaar" are anagrams. 

Constraints:

• 1 <= s.length <= 5 * 104
• s.length == t.length
• s and t consist of lowercase English letters only.

题解：

One swap is to make a char c which is not in t become a char in t.

Map to count occurance in s and not in t.

For every extra char, which count is +, it could be used to swap to a char in t but not in s, which is -.

Time Complexity: O(n). n = s.length().

Space: O(1).

AC Java:

 1 class Solution {
 2     public int minSteps(String s, String t) {
 3         int [] map = new int [26];
 4         for(int i = 0; i < s.length(); i++){
 5             map[s.charAt(i) - 'a']++;
 6             map[t.charAt(i) - 'a']--;
 7         }
 8         
 9         int res = 0;
10         for(int num : map){
11             if(num > 0){
12                 res += num;
13             }
14         }
15         
16         return res;
17     }
18 }

类似Minimum Number of Steps to Make Two Strings Anagram II.