[数据结构与算法]leetcode28. 实现 strStr() (java)

简单题朴素做法重拳出击

kmp还没学 嘻嘻

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

        for(int i = 0; i + n <= m; i ++){
            boolean flag = true;
            for(int j = 0; j < n; j ++){
                if(haystack.charAt(i + j) != needle.charAt(j)){
                    flag = false;
                    break;
                }
            }
            if(flag) {
                return i ; 
            }
        }
        return -1;
    }
}

这是kmp 我懂思想 写不出来 感谢官方题解

class Solution {
    public int strStr(String haystack, String needle) {
        int n = haystack.length(), m = needle.length();
        if (m == 0) {
            return 0;
        }
        int[] pi = new int[m];
        for (int i = 1, j = 0; i < m; i++) {
            while (j > 0 && needle.charAt(i) != needle.charAt(j)) {
                j = pi[j - 1];
            }
            if (needle.charAt(i) == needle.charAt(j)) {
                j++;
            }
            pi[i] = j;
        }
        for (int i = 0, j = 0; i < n; i++) {
            while (j > 0 && haystack.charAt(i) != needle.charAt(j)) {
                j = pi[j - 1];
            }
            if (haystack.charAt(i) == needle.charAt(j)) {
                j++;
            }
            if (j == m) {
                return i - m + 1;
            }
        }
        return -1;
    }
}

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