洛谷 || 二分算法：砍树

#include<iostream>

using namespace std;

const long long N = 1000000;
long long x, y, cleft, cright = 0, test = 0;
long long a[N];

int main() {
    cin >> x >> y;
    for (int i = 1; i <= x; i++) {
        cin >> a[i];
        if (a[i] > cright) {
            cright = a[i];//找最高值
        }
    }
    cleft = a[0];
    while (cleft <= cright) {
        long long mid = (cleft + cright) >> 1;//取中间值
        test = 0;
        for (int i = 1; i <= x; i++)
            if (mid < a[i])
                test += a[i] - mid;
        if (y > test) {
            cright = mid - 1;//左边 减小高度增加木材
        } else {
            cleft = mid + 1;//右边 增加高度减少木材
        }
    }
    cout << cleft - 1;
    return 0;
}