HDU 6153 拓展kmp

题意：

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=6153
Ni表示S串中出现了多少次T[i,len]，Li表示T[i,len]的长度，求Li和Ni的乘积和。

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思路：

把S和T都倒过来拓展KMP即可。

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代码：

#include <bits/stdc++.h>using namespace std;typedef long long LL;const LL MOD = 1e9 + 7;const int MAXN = 1e6 + 10;int nxt[MAXN], ext[MAXN];void getnext(char *T) {    int i, len = strlen(T), x = 1;    nxt[0] = len;    for (i = 0; i < len - 1 && T[i] == T[i + 1]; i++);    nxt[1] = i;    for (int k = 2; k < len; k++) {          int p = x + nxt[x] - 1, L = nxt[k - x];          if (k - 1 + L >= p) {               int j = max(p - k + 1, 0);               while (k + j < len && T[k + j] == T[j]) j++;               nxt[k] = j, x = k;          }          else nxt[k] = L;    }}void getextand(char *S, char *T, int ls, int lt){    memset(nxt, 0, sizeof(nxt));    getnext(T);    int x = 0, MinLen = min(ls, lt);    while (x < MinLen && S[x] == T[x]) x++;    ext[0] = x, x = 0;    for (int k = 1; k < ls; k++) {        int p = x + ext[x] - 1, L = nxt[k - x];        if ((k - 1) + L >= p) {           int j = max(p - k + 1, 0);           while (k + j < ls && j < lt && S[k + j] == T[j]) j++;           ext[k] = j; x = k;        }        else ext[k] = L;    }}int cnt[MAXN];char s[MAXN], t[MAXN], tmp[MAXN];int main() {    //freopen("in.txt", "r", stdin);    int T;    scanf("%d", &T);    while (T--) {        scanf("%s%s", s, t);        memset(cnt, 0, sizeof(cnt));        int ls = strlen(s), lt = strlen(t);        strcpy(tmp, s);        for (int i = 0; i < ls; i++) s[i] = tmp[ls - i - 1];        strcpy(tmp, t);        for (int i = 0; i < lt; i++) t[i] = tmp[lt - i - 1];        //cout << s << endl;        //cout << t << endl;        getextand(s, t, ls, lt);        for (int i = 0; i < ls; i++) ++cnt[ext[i]];        for (int i = lt - 1; i >= 1; i--) cnt[i] += cnt[i + 1];        LL ans = 0;        for (int i = 1; i <= lt; i++)            ans = (ans + (LL)cnt[i] * i % MOD) % MOD;        printf("%I64d\n",ans);    }    return 0;}