只是记录

方案一（一个段错误）

#include<iostream>
#include<cstring>
using namespace std;
const int N = 1e5+10;

int n, p[N], cnt[N];
int main()
{
    scanf("%d", &n);
    int maxday = 0;
    for(int i = 1; i <= n; i ++)
    {
        scanf("%d", &p[i]);
        if(p[i]) cnt[p[i]-1] += 1;
        maxday = max(maxday, p[i]);
    }
    int countN = 0;
    for(int i = maxday; i > 0; i --)
    {
        countN += cnt[i];
        //printf("countN is %d day is %d\n", countN, i);
        if(countN >= i)
        {
            printf("%d\n", i);
            return 0;
        }
    }
    printf("0\n");
    return 0;
}

方案而 （两个运行超时）

#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
const int N = 1e5+10;

int n, p[N], cnt[N];
int main()
{
    scanf("%d", &n);
    for(int i = 1; i <= n; i ++)
    {
        scanf("%d", &p[i]);
    }
    sort(p+1, p + n + 1);
    p[0] = p[1]-1;
    int j;
    for(int i = n; i >= 0; i = j)
    {
        if(p[i]) 
        {   
            j = i-1;
            while(p[j] == p[i])
                j--;
            cnt[j] = i-j+cnt[i];
            //printf("i is %d j is %d\n", i, j);
            //printf("p[i] is %d p[j] is %d cnt[i] is %d\n", p[i], p[j], cnt[i]);
        }
    } // small to big
    int countN = 0;
    for(int i = n; i >= 0; i = j)
    {
        j = i-1;
        while(p[j] == p[i])
            j--;
        int res = p[j+1];
        while(res != p[j])
        {
            //printf("count is %d day is %d\n", cnt[i], res);
            if(cnt[i] >= res)
            {
                printf("%d\n", res);
                return 0;
            }
            res -- ;
        }
    }
    printf("0\n");
    return 0;
}