HDOJ2087 剪花布条(kmp)

题目链接：点击打开链接

给出两个字符串，问你后面的字符串在前面的字符串中出现了几次。

求出小饰条的nxt数组，然后用花纹布匹配，每匹配成功一次j就归零一次，避免出现多次无用匹配的错误。

AC代码：

#include "iostream"
#include "cstdio"
#include "cstring"
#include "algorithm"
using namespace std;
const int MAXN = 1005;
char s1[MAXN], s2[MAXN];
int nxt[MAXN], len1, len2;
void get_nxt()
{
	nxt[1] = 0;
	int j = 0;
	for(int i = 2; i <= len2; ++i) {
		while(j > 0 && s2[j + 1] != s2[i])
			j = nxt[j];
		if(s2[j + 1] == s2[i]) j++;
		nxt[i] = j;
	}
}
int kmp()
{
	int j = 0, ans = 0;
	for(int i = 1; i <= len1; ++i) {
		while(j > 0 && s2[j + 1] != s1[i])
			j = nxt[j];
		if(s2[j + 1] == s1[i]) j++;
		if(j == len2) {
			ans++;
			j = 0;
		}
	}
	return ans;
}
int main(int argc, char const *argv[])
{
	while(scanf("%s", s1 + 1) != EOF && s1[1] != '#') {
		scanf("%s", s2 + 1);
		memset(nxt, 0, sizeof(nxt));
		len1 = strlen(s1 + 1), len2 = strlen(s2 + 1);
		get_nxt();
		printf("%d\n", kmp());
	}
	return 0;
}