KMP

​ KMP算法每当一趟匹配过程中出现字符比较不等时，主串S中的i指针不需回溯，而是利用已经得到的“部分匹配”结果将模式向右“滑动”尽可能远的一段距离后，继续进行比较。

​ KMP算法的主要核心其实就是next数组的求解

next数组求解

void GetNext(char *w, int next[])
{//w为模式串memset(next, 0, sizeof(next));int i, j, len;i = 0;j = -1;next[0] = -1;len = strlen(w);while(i < len){if(j == -1 || w[i] == w[j]){i++;j++;if(w[i] != w[j])next[i] = j;elsenext[i] = next[j];}else    j = next[j];}
}

字符串匹配

int kmp(char *s, char *p, int next[])
{int s_len = strlen(s);int p_len = strlen(p);int i = 0;int j = 0;int cnt  = 0;while(i < s_len && j < P_len){if(j == -1 || s[i] == p[j]){i++;j++;}else    j = next[j];}if(j == p_len)	return i-j;else			return -1;
}

总代码

#include<stdio.h>
#include<string.h>
int next[1000005];
char w[1000005];
char t[1000005];
void GetNext(char *w, int next[])
{memset(next, 0, sizeof(next));int i, j, len;i = 0;j = -1;next[0] = -1;len = strlen(w);while(i < len){if(j == -1 || w[i] == w[j]){i++;j++;if(w[i] != w[j])next[i] = j;elsenext[i] = next[j];}else    j = next[j];}
}
int kmp(char *s, char *p, int next[])
{int s_len = strlen(s);int p_len = strlen(p);int i = 0;int j = 0;while(i < s_len && j < p_len){if(j == -1 || s[i] == p[j]){i++;j++;}else    j = next[j];}if(j == p_len)  return i - j;else            return -1;
}
int main()
{scanf("%s", w);scanf("%s", t);GetNext(w, next);if(kmp(t, w, next) != -1)     printf("匹配成功\n");else                          printf("匹配失败\n");return 0;
}