LeetCode 28. Implement strStr() Java

最新推荐文章于 2020-07-28 17:59:33 发布

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本文提供了一个字符串匹配算法的具体实现，该算法用于寻找一个字符串（haystack）中另一个字符串（needle）首次出现的位置。若找到则返回该位置的索引，否则返回-1。文章通过示例展示了如何使用该算法，并对特殊情况进行了说明。

水题

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

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

Example 2:

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

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

class Solution {
    public int strStr(String haystack, String needle) {
        int lenA=haystack.length();
        int lenB=needle.length();
        if(lenA<lenB)
            return -1;
        int index=0;
        while(true){
            String str=haystack.substring(index,index+lenB);
            if(needle.equals(str))
                return index;
            index++;
            if((index+lenB)>lenA)
                break;
        }
        return -1;
    }
}