Codeforces 39J Spelling Check hash

意甲冠军：

特定2弦

选择中删除一个字符串的第一个字母，得2个字符串全然同样

问哪些位置能够选

思路：

hash求前缀后缀。然后枚举位置

#include <cstdio>
#include <algorithm>
#include<iostream>
#include<string.h>
#include <math.h>
#include<queue>
#include<map>
#include<vector>
#include<set>
using namespace std;
#define mod 100000007
#define ll long long
#define N 1000050
char s[N], c[N];
vector <int> ans;
ll l1[N], r1[N], l2[N], r2[N];
int main(){
    int i, j;
    while(~scanf("%s",s+1)){
        scanf("%s",c+1);
        int len1 = strlen(s+1), len2 = strlen(c+1);
        if(len1 -1 != len2){puts("0");continue;}
        l1[0] = 0;
        for(i = 1; i <= len1; i++) {
            l1[i] = l1[i-1]*26 + s[i];
            if(l1[i]>=mod) l1[i] %= mod;
        }
        r1[len1+1] = 0;
        for(i = len1; i ; i--) {
            r1[i] = r1[i+1]*26 + s[i];
            if(r1[i]>=mod) r1[i] %= mod;
        }

        l2[0] = 0;
        for(i = 1; i <= len2; i++) {
            l2[i] = l2[i-1]*26 + c[i];
            if(l2[i]>=mod) l2[i] %= mod;
        }
        r2[len2+1] = 0;
        for(i = len2; i ; i--) {
            r2[i] = r2[i+1]*26 + c[i];
            if(r2[i]>=mod) r2[i] %= mod;
        }
        ans.clear();
        for(i = 1; i <= len1; i++) {
            ll a = l1[i-1] + r1[i+1];
            ll b = l2[i-1]+r2[i];
            if(a==b)ans.push_back(i);
        }

        cout<<ans.size()<<endl;
        for(i = 0; i <ans.size(); i++)
            printf("%d%c", ans[i], i==ans.size()-1?'
':' ');
    }
    return 0;
}