light oj 1255 - Substring Frequency (KMP)

//light oj 1255 - Substring Frequency (KMP)
//2013-05-13-19.12
#include <stdio.h>
#include <string.h>
const int maxn = 1000006;

char a[maxn];
char b[maxn];
int f[maxn];

void getfail()
{
    int l = strlen(b);
    f[0] = 0;
    f[1] = 0;
    for (int i = 1; i < l; i++)
    {
        int j = f[i];
        while (j && b[i] != b[j])
            j = f[j];
        if (b[i] == b[j])
            f[i+1] = j+1;
        else
            f[i+1] = 0;
    }
}

int kmp()
{
    int ans = 0;
    int la = strlen(a);
    int lb = strlen(b);
    getfail();
    int j = 0;
    for (int i = 0; i < la; i++)
    {
        while (j && a[i] != b[j])
            j = f[j];
        if (b[j] == a[i])
            j++;
        if (j == lb)
            ans++;
    }
    return ans;
}

int main()
{
    int t;
    scanf("%d", &t);
    for (int i = 1; i <= t; i++)
    {
        scanf("%s %s", a, b);
        printf("Case %d: %d\n", i, kmp());
    }
    return 0;
}