A30168.砍伐树木

二分答案，但是记得开long long！！！（不开70分）

#include <iostream>
#include <algorithm>
using namespace std;
typedef long long ll;

int n, m;
int a[1000005];

bool check(int ans) {
    ll cnt = 0;
    for (int i=1; i<=n; i++) {
        cnt += (a[i]>ans?a[i]-ans:0);
    }
    return cnt >= m;
}

int main() {
    cin >> n >> m;
    for (int i=1; i<=n; i++) cin >> a[i];
    ll l = 0, r = 2e9, ans = 0;
    while (l <= r) {
        ll mid = l+r>>1;
        if (check(mid)) l = mid+1, ans = mid;
        else r = mid-1;
    }
    cout << ans;
    return 0;
}