Python、java、go实现"strStr()"的几种方法

实现strStr()

输入haystack和needle两个字符串，返回haystack中第一次出现needle字符串的索引下标。如果不存在，返回-1

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

说明：当needle为空时，返回0

1：利用字符串自带的str.find()方法返回满足条件的索引下标

def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle:
            return 0
        return haystack.find(needle)

2：遍历haystack字符串，判断是否匹配needle字符串，返回对应结果

def strStr(self, haystack, needle):
        """
        :type haystack: str
        :type needle: str
        :rtype: int
        """
        if not needle:
            return 0
        if needle not in haystack:
            return -1
        else:
            for index in range(len(haystack)):
                if haystack[index:index+len(needle)]==needle:
                    return index

上面是 python 实现，下面是 java 实现的版本

public int strStr(String haystack, String needle) {
        if (needle.length() > haystack.length()) {
            return -1;
        }
        int hayLen = haystack.length();
        int neeLen = needle.length();
        for (int i = 0; i + neeLen <= hayLen; i++) {
            if (haystack.substring(i,i+neeLen).equals(needle)) {
                return i;
            }
        }
        return -1;
        //return haystack.indexOf(needle);
    }

以下是 go 实现版本

func strStr(haystack string, needle string) int {
	if len(needle) > len(haystack) {
		return -1
	}
	for head := 0; head + len(needle) <= len(haystack); head++ {
		if haystack[head:head+len(needle)] == needle {
			return head
		}
	}
	return -1
}

算法题来自：https://leetcode-cn.com/problems/implement-strstr/description/