13. strStr

Description

For a given source string and a target string, you should output the first index(from 0) of target string in source string.
If target does not exist in source, just return -1.

Analysis

难
2h of thinking

Code

class Solution {
    /**
     * Returns a index to the first occurrence of target in source,
     * or -1  if target is not part of source.
     * @param source string to be scanned.
     * @param target string containing the sequence of characters to match.
     */
    public int strStr(String source, String target) {
        //write your code here
        
        if (source == null || target == null) {
            return -1;
        } 
        if (target == "") {
            return 0;
        }
        if (source == "") {
            return -1;
        }

        int start = 0;
        // 如果剩下的字母不够needle长度就停止遍历
        while(start <= source.length() - target.length()){
            int i1 = start, i2 = 0;
            while(i2 < target.length() && source.charAt(i1) == target.charAt(i2)){
                i1++;
                i2++;
            }
            if(i2 == target.length()) return start;
            start++;
        }

        return -1;
    }
}