Codeforces 985 D - Sand Fortress

D - Sand Fortress

思路：

二分

有以下两种构造，

分别二分取个最小。

代码：

#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
//#define mp make_pair
#define pb push_back
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pii pair<int, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);
//head
ULL n, h;
bool check(ULL t) {
    ULL res;
    if(t >= h) res = (+t)*t/ + t*(t-)/ - h*(h-)/;
    else res = (+t)*t/;
    if(res >= n) return true;
    else return false;
}
bool Check(ULL t) {
    ULL res;
    if(t >= h) res = (+t)*t - h*(h-)/;
    else res = (+t)*t/;
    if(res >= n) return true;
    else return false;
}
int main() {
    scanf("%llu%llu", &n, &h);
    ULL l = , r = 2e9, m = (l+r) >> ;
    while(l < r) {
        if(check(m)) r = m;
        else l = m+;
        m = (l+r) >> ;
    }
    ULL ans;
    if(m >= h) ans = *m - h;
    else ans = m;
    l = , r = 2e9, m = (l+r) >> ;
    while(l < r) {
        if(Check(m)) r = m;
        else l = m+;
        m = (l+r) >> ;
    }
    if(m >= h) ans = min(ans, *m - h + );
    else ans = min(ans, m);
    printf("%llu\n", ans);
    return ;
}