A and B and Interesting Substrings - CodeForces 519 D dp

最新推荐文章于 2020-03-14 18:24:31 发布

提比-我有特殊的AC技巧

最新推荐文章于 2020-03-14 18:24:31 发布

阅读量629

点赞数

CC 4.0 BY-SA版权

分类专栏： dp动态规划和递推 CodeForces

本文链接：https://blog.youkuaiyun.com/u014733623/article/details/44014433

dp动态规划和递推同时被 2 个专栏收录

281 篇文章

订阅专栏

CodeForces

82 篇文章

订阅专栏

本文介绍了一种算法，用于计算给定字符串中符合特定条件的子串数量。这些子串需首尾字母相同且中间字母的权值和为0。通过使用哈希表记录每个字母在不同累计权值下出现的次数，实现快速查找。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

A and B are preparing themselves for programming contests.

After several years of doing sports programming and solving many problems that require calculating all sorts of abstract objects, A and B also developed rather peculiar tastes.

A likes lowercase letters of the Latin alphabet. He has assigned to each letter a number that shows how much he likes that letter (he has assigned negative numbers to the letters he dislikes).

B likes substrings. He especially likes the ones that start and end with the same letter (their length must exceed one).

Also, A and B have a string s. Now they are trying to find out how many substrings t of a string s are interesting to B (that is, t starts and ends with the same letter and its length is larger than one), and also the sum of values of all letters (assigned by A), except for the first and the last one is equal to zero.

Naturally, A and B have quickly found the number of substrings t that are interesting to them. Can you do it?

Input

The first line contains 26 integers xa, xb, ..., xz ( - 105 ≤ xi ≤ 105) — the value assigned to letters a, b, c, ..., z respectively.

The second line contains string s of length between 1 and 105 characters, consisting of Lating lowercase letters— the string for which you need to calculate the answer.

Output

Print the answer to the problem.

Sample test(s)

input
1 1 -1 1 1 1 1 1 1 1 1 1 1 1 1 7 1 1 1 8 1 1 1 1 1 1
xabcab

output
2

input
1 1 -1 1 1 1 1 1 1 1 1 1 1 1 1 7 1 1 1 8 1 1 1 1 1 1
aaa

output
2

题意：求有多少个连续子序列的首尾字母相同，并且中间的字母的权值和为0。

思路：match[i][j]表示字母i在前面有多少个前缀权值为j的情况。

AC代码如下：

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cmath>
#include<map>
using namespace std;
typedef long long ll;
map<ll,ll> match[30];
ll ans,val[30];
int T,t,n,m,num[100010],temp[100010];
char s[100010];
int main()
{
    int i,j,k;
    ll ret=0;
    for(i=1;i<=26;i++)
       scanf("%I64d",&val[i]);
    scanf("%s",s+1);
    n=strlen(s+1);
    for(i=1;i<=n;i++)
    {
        j=s[i]-'a'+1;
        ans+=match[j][ret];
        ret+=val[j];
        match[j][ret]++;
    }
    printf("%I64d\n",ans);
}