【Leetcode 28】 实现strStr()

方法1：

python版本

class Solution:
    def strStr(self, haystack: str, needle: str) -> int:
        c=-1
        for i in range(len(haystack)-len(needle)+1):
            if haystack[i:i+len(needle)]==needle:
                c=i
                break
        return c

java版本

class Solution {
  public int strStr(String haystack, String needle) {
    int L = needle.length(), n = haystack.length();

    for (int start = 0; start < n - L + 1; ++start) {
      if (haystack.substring(start, start + L).equals(needle)) {
        return start;
      }
    }
    return -1;
  }
}

注意时间复杂度，总共得比较次数是N-L+1次，这里把常数级给忽略掉了

方法2：使用KMP算法
​​​ https://leetcode-cn.com/problems/implement-strstr/solution/kmp-suan-fa-xiang-jie-by-labuladong/​​

题目参考链接
​​​ https://leetcode-cn.com/problems/implement-strstr/solution/shi-xian-strstr-by-leetcode/​​