leetcode28. 找出字符串中第一个匹配项的下标_简单KMP

 28. 找出字符串中第一个匹配项的下标 - 力扣（LeetCode）

模仿：algorithm-journey/src/class100/Code01_KMP.java at main · algorithmzuo/algorithm-journey · GitHub

#include <stdio.h>
#include <stdlib.h>
#include <string.h>void getNext(char *s, int m, int *next) {if (m == 1) {next[0] = -1;return;}next[0] = -1;next[1] = 0;int i = 2, cn = 0;while (i < m) {if (s[i - 1] == s[cn]) {next[i++] = ++cn;} else if (cn > 0) {cn = next[cn];} else {next[i++] = 0;}}
}int kmp(char *s1, char *s2) {int n = strlen(s1), m = strlen(s2);int x = 0, y = 0;int *next = (int *)malloc(m * sizeof(int));getNext(s2, m, next);while (x < n && y < m) {if (s1[x] == s2[y]) {x++;y++;} else if (y == 0) {x++;} else {y = next[y];}}free(next);return y == m ? x - y : -1;
}int strStr(char *haystack, char *needle) {return kmp(haystack, needle);
}

 官方题解：

C++

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

C：

int strStr(char* haystack, char* needle) {int n = strlen(haystack), m = strlen(needle);if (m == 0) {return 0;}int pi[m];pi[0] = 0;for (int i = 1, j = 0; i < m; i++) {while (j > 0 && needle[i] != needle[j]) {j = pi[j - 1];}if (needle[i] == needle[j]) {j++;}pi[i] = j;}for (int i = 0, j = 0; i < n; i++) {while (j > 0 && haystack[i] != needle[j]) {j = pi[j - 1];}if (haystack[i] == needle[j]) {j++;}if (j == m) {return i - m + 1;}}return -1;
}

待定