CF #727（div2）B. Love Song，前缀和

Posted 2021-06-30 小哈里

problem

B. Love Song
time limit per test2 seconds
memory limit per test256 megabytes
inputstandard input
outputstandard output
Petya once wrote a sad love song and shared it to Vasya. The song is a string consisting of lowercase English letters. Vasya made up q questions about this song. Each question is about a subsegment of the song starting from the l-th letter to the r-th letter. Vasya considers a substring made up from characters on this segment and repeats each letter in the subsegment k times, where k is the index of the corresponding letter in the alphabet. For example, if the question is about the substring “abbcb”, then Vasya repeats letter ‘a’ once, each of the letters ‘b’ twice, letter 'c" three times, so that the resulting string is “abbbbcccbb”, its length is 10. Vasya is interested about the length of the resulting string.

Help Petya find the length of each string obtained by Vasya.

Input
The first line contains two integers n and q (1≤n≤100000, 1≤q≤100000) — the length of the song and the number of questions.

The second line contains one string s — the song, consisting of n lowercase letters of English letters.

Vasya’s questions are contained in the next q lines. Each line contains two integers l and r (1≤l≤r≤n) — the bounds of the question.

Output
Print q lines: for each question print the length of the string obtained by Vasya.

Examples
inputCopy
7 3
abacaba
1 3
2 5
1 7
outputCopy
4
7
11
inputCopy
7 4
abbabaa
1 3
5 7
6 6
2 4
outputCopy
5
4
1
5
inputCopy
13 7
sonoshikumiwo
1 5
2 10
7 7
1 13
4 8
2 5
3 9
outputCopy
82
125
9
191
62
63
97
Note
In the first example Vasya is interested in three questions. In the first question Vasya considers the substring “aba”, that transforms to “abba”, so the answer is equal to 4. In the second question Vasya considers “baca”, that transforms to “bbaccca”, so the answer is 7. In the third question Vasya considers the string “abacaba”,that transforms to “abbacccabba” of length 11.

solution

#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 100010;
vector<int>z[maxn];
int main(){
	int n, q;  cin>>n>>q;
	string s;  cin>>s; s="0"+s;
	z[0].resize(27);
	for(int i = 1; i <= n; i++){
		z[i].resize(27);
		z[i] = z[i-1];
		z[i][s[i]-'a']++;
	}
	while(q--){
		int l, r;  cin>>l>>r;
		LL ans = 0;
		for(int i = 0; i < 26; i++){
			ans += (z[r][i]-z[l-1][i])*1LL*(i+1);
		}
		cout<<ans<<"\\n";
	}
	return 0;
}