大抵是二分前没初始化完全罢

比如,像这样：

ll l = 0, r = 1e18, ans;
while(l <= r){
	ll mid = (l + r) >> 1;
	if(check(mid)){
		r = mid - 1;
		ans = mid;
	}else{
		l = mid + 1;
	}
}

改成这样即可：

ll l = 0, r = 1e18, ans = 1e18;
while(l <= r){
	ll mid = (l + r) >> 1;
	if(check(mid)){
		r = mid - 1;
		ans = mid;
	}else{
		l = mid + 1;
	}
}