HDU1686 Oulipo（扩展KMP）

来源：互联网发布：linux 鸟哥的私房菜编辑：程序博客网时间：2024/05/29 16:48

题意：给出两个串w和t，求w在t中出现的次数，不同次数可以覆盖。

思路：可以做一次扩展KMP，求出以t的每一位作起点与w的匹配长度，然后扫一遍结果，达到w的长度就加一。

#include<iostream>#include<cstdio>#include<cstring>#include<cmath>#include<cstdlib>#include<vector>#include<map>#include<algorithm>using namespace std;typedef long long ll;const int inf = 0x3f3f3f3f;const int mod = 1000000007;const int maxn = 1000005;int extend[maxn], nxt[10005];void get_next(char str[]){    int i = 0, j, pos;    int len = strlen(str);    nxt[0] = len;    while(i + 1 < len && str[i] == str[i + 1]){        ++i;    }    nxt[1] = i;    pos = 1;    for(i=2; i<len; ++i){        if(nxt[i - pos] < pos + nxt[pos] - i){            nxt[i] = nxt[i - pos];        } else {            j = nxt[pos] + pos - i;            if(j < 0){                j = 0;            }            while(i + j < len && str[i + j] == str[j]){                ++j;            }            nxt[i] = j;            pos = i;        }    }}void EXKMP(char target[], char pattern[]){    int i = 0, j, pos;    get_next(pattern);    int len1 = strlen(target);    int len2 = strlen(pattern);    while(i < len1 && i < len2 && target[i] == pattern[i]){        ++i;    }    extend[0] = i;    pos = 0;    for(i=1; i<len1; ++i){        if(nxt[i - pos] < pos + extend[pos] - i){            extend[i] = nxt[i - pos];        } else {            j = extend[pos] + pos - i;            if(j < 0){                j = 0;//从头匹配            }            while(i + j < len1 && j < len2 && target[i + j] == pattern[j]){                ++j;            }            extend[i] = j;            pos = i;//更新pos        }    }}char w[10005], t[maxn];int main(){    int T;    scanf("%d", &T);    while(T--){        scanf("%s%s", w, t);        EXKMP(t, w);        int ans = 0;        int l1 = strlen(t);        int l2 = strlen(w);        for(int i = 0; i < l1; ++i){            if(extend[i] == l2){                ++ans;            }        }        printf("%d\n", ans);    }    return 0;}

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