百度之星-day2-1004-二分答案

  由于序列有序，求其中一个最优解，二分答案即可，注意二分时上边界满足才保存

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<algorithm>
#define ll long long
using namespace std;
const int maxx = 300005;
ll a[maxx];
ll l,r;
ll pre[maxx];
int main()
{
    int t;
    ll ans=0;
    ll n;
    scanf("%d",&t);
    while(t--)
    {
        ans=0;
        scanf("%lld",&n);
        for (int i=1; i<=n; i++)
        {
            scanf("%lld",&a[i]);
        }
        sort(a+1,a+1+n);
        ll r=100000000;
        ll l=0;
        ll mid=0;
        ll pr=0,ba=0;
        while(l<=r)
        {
            pr=0;
            ba=0;
            mid=(l+r)/2;
            for (int i=1; i<=n; i++)
            {
                if (a[i]<mid)
                {
                    pr+=(mid-a[i]);//左边和
                }
                else if (a[i]>mid)
                {
                    ba+=((a[i]-mid)/2);//右边和
                }
             }
             if (ba>=pr){//如果满足条件答案才被记录下来
                ans=mid;
                l=mid+1;
                continue;
             }else {
                r=mid-1;//不满足就继续向上查找
                continue;
             }
         }
         printf("%lld\n",ans);
    }
  return 0;
}