P8577 [CoE R5] 暴龙的白菜 题解
Description
有一个字符串，由 \(\texttt{1}\) 个 \(\texttt{1}\)，\(\texttt{2}\) 个 \(\texttt{2}\)，\(\texttt{3}\) 个 \(\texttt{3}\)......组成。
现有 \(m\) 次询问，问从第 \(l\) 到第 \(r\) 位上数字之和。
Solution
本题数据范围很重要：\(0\le l\le r\le10^6\)。
计算可得，字符串数最多在 \(\texttt{1000}\) 和 \(\texttt{1050}\) 之间，预处理即可。
再遍历一遍字符串，记录前缀和即可。
Code
#include<bits/stdc++.h>
using namespace std;
int sum[1000100];
string s;
int t;
string ss[1200]={" 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int read(){
int x=0,f=1;
char ch;
ch=getchar();
while(ch<'0'||ch>'9'){
if(ch=='-') f=-1;
ch=getchar();
}
while(ch>='0'&&ch<='9'){
x=x*10+ch-'0';
ch=getchar();
}
return x*f;
}
int main(){
for(int i=1;i<=1100;i++){
for(int j=1;j<=i;j++){
s+=ss[i]; //预处理字符串
}
}
sum[0]=0;
for(int i=1;i<=1000000;i++){
sum[i]=sum[i-1]+s[i-1]-'0'; //预处理前缀和
}
t=read();
while(t--){
int l=read(),r=read();
printf("%d\n",sum[r]-sum[l-1]);
}
return 0;
}
