字符串匹配的KMP算法（不建议大家看，这里是我的暂时笔记）

做个记录：

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <string>

using namespace std;
const int maxn = 1000;

int Next[maxn];
string pattern, target;

void produceNext() {
int i = 0, j = -1, len = pattern.length();
Next[0] = -1;
while (i < len) {
if (pattern[++i] != pattern[++j]) {
Next[i] = j;
while (j != -1 && pattern[i] != pattern[j]) j = Next[j];
} else {
Next[i] = Next[j];
}
}
}

int KMP() {
int i = 0, j = 0, sum = 0, len1 = target.length(), len2 = pattern.length();

while (len2 - j <= len1 - i) {
if (pattern[j] == target[i]) {
i++;
j++;
if (j == len2) sum++;
} else {
j = Next[j];
if (j == -1) {
i++;
j++;
}
}
}
return sum;
}

int main() {
puts("请输入目标串，以及模式串（不包含空格）：");
cin >> target >> pattern;
produceNext();
cout << "一共有：" << KMP() << " 个匹配值。" << endl;
cout << "haha " << endl;
return 0;
}