查找子串出现在原字符串第一次的索引
没找到返回1
public int strStr(String haystack, String needle) { if (haystack.length() < needle.length()) return -1; if (needle.length() == 0) return 0; int[] next = getNext(needle); for (int i = 0, j = 0; i < haystack.length(); i++) { while (j > 0 && haystack.charAt(i) != needle.charAt(j)) { j = next[j - 1]; } if (haystack.charAt(i) == needle.charAt(j)) { j++; } if (j == needle.length()) { return i - j + 1; } } return - 1; } //获取子串的部分匹配表 public int[] getNext(String needle) { int[] next = new int[needle.length()]; next[0] = 0; for (int i = 1, j = 0; i < needle.length(); i++) { while (j > 0 && needle.charAt(i) != needle.charAt(j)) { j = next[j - 1]; } if (needle.charAt(i) == needle.charAt(j)) { j++; } next[i] = j; } return next; }