Implement strStr()(目标字符串在原字符串的位置)leetcode28

男娘i 2022-05-23 07:45 104阅读 0赞

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Implement [strStr()][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()][strStr] and Java's [indexOf()][indexOf].

code1:

public int strStr(String haystack, String needle) {
            //return haystack.indexOf(needle);
            if(needle.isEmpty())
                return 0;
            int j=0;
            for(int i=0;i<haystack.length();){
                if(j<needle.length()&&haystack.charAt(i)==needle.charAt(j)){
                    if(j==needle.length()-1)
                        return i-j;
                    j++;
                    i++;
                }else{
                     i=i-j+1;
                     j=0;
               }
            }
            return -1;
        }

code2:

public int strStr(String haystack, String needle) {
                for (int i = 0; ; i++) {
                    for (int j = 0; ; j++) {
                        if (j == needle.length()) return i;
                        if (i + j == haystack.length()) return -1;
                        if (needle.charAt(j) != haystack.charAt(i + j)) break;
        
                    }
      
                }
    
            }

[strStr]: http://www.cplusplus.com/reference/cstring/strstr/
[indexOf]: https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf%28java.lang.String%29