Codeforces 39j spelling check Hash

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Question:

2 strings

Delete one of the first strings so that the two strings are identical.

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Ideas:

Calculate the prefix and Suffix in hash, and then enumerate the positions

#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 1000050char 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?'\n':' ');    }    return 0;}