[백준 2805] 나무 자르기 (Binary Search) (C/C++) (★)

#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <string>
#include <string.h>
#include <math.h>
#include <map>
#include <vector>
using namespace std;
 
int N, M;
long long Max;
long long tree[1000010];
 
long long cal(long long mid)
{
    long long sum = 0;
    
    for(int i = 1; i <= N; i++)
    {
        if(mid < tree[i])
        {
            sum += tree[i]-mid;
        }
    }
    
    return sum;
}
 
int main(void)
{
//    freopen("B2805_input.txt", "r", stdin);
    
    cin >> N >> M;
    
    for(int i = 1; i <= N; i++)
    {
        cin >> tree[i];
    }
    
    sort(tree+1, tree+N+1);
    
    long long left = 1;
    long long right = tree[N];
    
    while(left <= right)
    {
        // 절단기의 높이 
        long long mid = (left + right) / 2;
        
        // 자른 나무길이의 합 
        long long sum = cal(mid);
        
        if(sum >= M)
        {
            left = mid+1;
            
            if(mid > Max)
            {
                Max = mid;
            }
        }
        else
        {
            right = mid-1;
        }
    }
    
    cout << Max;
    
    return 0;
}