HDU 4300 KMP

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <cctype>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <algorithm>
#include <iostream>
#include <string>
#include <set>
#define X first
#define Y second
#define sqr(x) (x)*(x)
#pragma comment(linker,"/STACK:102400000,102400000")
using namespace std;
const double PI = acos(-1.0);
map<int, int>::iterator it;
typedef long long LL ;
template<typename T> void checkmin(T &x, T y) {x = min(x, y);}
template<typename T> void checkmax(T &x, T y) {x = max(x, y);}

const int N = 100005;
int p[N];
int KMP(char *a, int n, char *b, int m) {
    p[0] = -1;
    int i, j = -1;
    for(i = 1; i <= m; i++) {
        while((j > -1) && (b[j+1] != b[i]))
            j = p[j];
        if(b[j+1] == b[i]) j++;
        p[i] = j;
    }
    //for(i=0;i<m;i++) printf("%d   ",p[i]); printf("\n");
    j = -1;
    for(i = 0; i < n; i++) {
        while((j > -1) && (b[j+1] != a[i])) j = p[j];
        if(b[j+1] == a[i]) {
            j++;
        }
        if(j == m - 1) {
            //printf("i=%d\n",i);
            //return i-m+1;
            j = p[j];
        }
    }
    return -1;
}
char mp[27],back[256];
char s[N], t[N];
int main() {
    int T;
    scanf("%d", &T);
    while(T--) {
        scanf("%s%s", mp, s);
        for(int i=0;i<26;++i)
        {
            back[ mp[i] ]='a'+i;
        }
        int n = strlen(s);
        strcpy(t, s);
        int m = 0;
        for(int i = (n + 1) / 2; i < n; ++i) {
            ++m;
            s[i] = mp[ s[i] - 'a' ];
        }
        KMP(s, n, s, n);
        /*
        for(int i = 0; i < n; ++i) {
            printf("%3c", s[i]);
        } puts("");
        for(int i = 0; i < n; ++i) {
            printf("%3d", p[i]);
        } puts("");
        */
        int len = 0, q = n - 1;
        while(~p[q])--q, ++len;
        //printf("len =%d\n", len);
        len = min(len, m);
        printf("%s", t);
        for(int i = len; i < n - len ; ++i) {
            printf("%c", back[t[i]]);
        } puts("");
    }
    return 0;
}