1117 Eddington Number (二分)

link

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>
#include <cstring>
#include <set>
#include <unordered_map>
#include <cmath>
# define LL long long
using namespace std;


int N;
vector<int> dis;

int find(int n){
    //找第一个比n大的数
    int left=0;
    int right=N-1;
    while(left<=right){
        int mid=(left+right)/2;

        if(dis[mid]>n){
            right=mid-1;
        }else{
            left=mid+1;
        }
    }
    if(left>N-1) return 0;
    return N-left;
}

int main(){
    scanf("%d", &N);
    for(int i=0;i<N;i++){
        int a;
        scanf("%d", &a);
        dis.push_back(a);
    }
    sort(dis.begin(), dis.end());
    int left=0;
    int right=N;
    while(left<=right){
        int mid=(left+right)/2;
        int nums=find(mid);
        //最大的满足nums==mid
        if(nums==mid){
            left=mid+1;
        }else if(nums<mid){
            right=mid-1;
        }else {
            left=mid+1;
        }
    }
    printf("%d\n", right);
    return 0;
}