A.Easy h-index

1 A. Easy h-index

The h-index of an author is the largest h where he has at least h papers with citations not less than h.
Bobo has published many papers. Given a0,a1,a2,…,an which means Bobo has published ai papers with
itations exactly i, find the h-index of Bobo.

1.1 Input

The input consists of several test cases and is terminated by end-of-file.
The first line of each test case contains an integer n. The second line contains (n+1) integers a0,a1,…,an.

1.2 Output

For each test case, print an integer which denotes the result.

1.3 Constraint

• 1≤ n ≤2·105 • 0≤ ai ≤109 • The sum of n does not exceed 250,000.

1.4 Sample Input

1
1 2
2
1 2 3
3
0 0 0 0

1.5 Sample Output

1
2
0

题意：给定被引用次数为 0~n 的论文分别有几张，找到最大的 h，满足被引用次数大于等于 h 的论文至少有 h 张
思路：在区间 [0,n] 内二分答案；或直接从 n~0 遍历找到第一个满足条件的 h

后 AC 代码

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#include "bits/stdc++.h"
using namespace std;
int main(){
    int a[200005];
    int n;
    int i;
    while(cin>>n){
        for(i=0;i<=n;i++)
            cin>>a[i];
        int sum=a[n];
        for(i=n;i>=0;){
            if(sum>=i){
                cout<<i<<endl;
                break;
            }
            else sum+=a[--i];
        }
        if(i<0)
            cout<<"0"<<endl;
    }
    return 0;
}