Convoy

Convoy

 

 二分基本题目

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstring>
#include <cmath>
#include <queue>
#include <stack>
#include <vector>
#include <set>
#include <map>
#include <sstream>
#include <algorithm>
using namespace std;
typedef long long ll;
const int maxn=2e4+9;
const ll mod=(ll)(1e9+7);

ll a[maxn],n,k;
bool judge(ll mid){///总时长
    ll ans=0,num;
    for(ll i=0;i<min(n,k);i++){
        num=mid/a[i];///在在该时长可以跑得趟数
        if( num>=1 ){
            ans += (num-1)/2*4+5;///最后一趟过来送了5个人,其他的自己还在上面坐着,来回送4个人
        }
        else break;
    }
    if( ans>=n ) return 1;
    return 0;
}

int main()
{
    ll i,j,m,left,right,ans;
    scanf("%lld %lld",&n,&k);
    for(i=0;i<n;i++){
        scanf("%lld",&a[i]);
    }
    sort(a,a+n);
    left=1;
    right=2e10;
    ans=2e11;
    while( left<=right ){
        ll mid=(left+right)/2;
        if( judge(mid) ){
            ans=min(ans,mid);
            right=mid-1;
        }
        else left=mid+1;
    }
    printf("%lld
",ans);
    return 0;
}