洛谷P1873 砍树 二分答案

洛谷P1873 砍树

二分答案

与原来的二分差不多
O(n) 判断 当然也可以小优化一下 将 h 从高到低排序
这题要用long long 感觉不大保险，于是全部都加了long long

#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <string>
#include <iomanip>
#include <iostream> 
#define ll long long 
using namespace std ; 

inline ll read() 
{
    char ch = getchar() ; 
    ll x = 0 , f = 1 ; 
    while(ch<'0'||ch>'9') { if(ch=='-') f = -1 ; ch = getchar() ; }
    while(ch>='0'&&ch<='9') { x = x*10 + ch - 48 ; ch = getchar() ; } 
    return x*f ; 
}

const int maxn = 1000011 ; 
ll n,m,l,r,mid ;
ll h[maxn] ; 

inline bool check(ll x) 
{
    ll sum = 0 ;
    for(int i=1;i<=n;i++) 
        if(h[ i ]>x) sum = sum + h[ i ]-x ; 
    return sum >= m ;
}

int main() 
{
    n = read() ;   m = read() ;  
    for(int i=1;i<=n;i++) 
        h[ i ] = read(),r = max(r,h[ i ]) ;  
    l = 0 ;  
    while( l < r ) 
    {
        mid = (l+r+1) / 2 ; 
        if( check(mid) ) 
            l = mid ; 
        else 
            r = mid - 1 ; 
    }
    printf("%lld
",l ) ; 
    return 0 ; 
}