[Ybt Advanced 2-3-1] Substring search

Substring search

Topic link: ybt efficient advanced 2-3-1

Topic

Find the number of occurrences of a string in another string.

Ideas

This question seems to be a KMP template question.

Just press the KMP template and type it again.

Code

#include<cstdio>
#include<cstring>

using namespace std;

int an, bn, ans, fail[1000001], j;
char a[1000001], b[1000001];

int main() {
    
    
	scanf("%s", a + 1);
	scanf("%s", b + 1);
	an = strlen(a + 1);
	bn = strlen(b + 1);
	
	j = 0;
	for (int i = 2; i <= bn; i++) {
    
    
		while (j && b[i] != b[j + 1]) j = fail[j];
		if (b[i] == b[j + 1]) j++;
		fail[i] = j;
	}
	
	j = 0;
	for (int i = 1; i <= an; i++) {
    
    
		while (j && a[i] != b[j + 1]) j = fail[j];
		if (a[i] == b[j + 1]) j++;
		if (j == bn) {
    
    
			ans++;
		}
	}
	
	printf("%d", ans);
	
	return 0;
}