April Fools Day Contest 2019 A. Thanos Sort题解

愚人节专场比我想象的难一些（太菜了）

代码来自一个博客：https://blog.youkuaiyun.com/qq_38185591/article/details/88966801

题目链接：https://codeforces.com/contest/1145/problem/A

主要考验dfs能力，我第一次写了110行代码没过卡题

贴代码：

#include<algorithm>
#include <iostream>
#include  <sstream>
#include  <cstring>
#include  <cstdlib>
#include   <string>
#include   <vector>
#include   <cstdio>
#include   <math.h>
#include    <queue>
#include    <stack>
#include      <set>
#include      <map>
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define rep(i,a,n) for (int i = a; i < n; ++i)
#define per(i,a,n) for (int i = n-1; i >= a; --i)
#define SZ(x) ((int)x.size())
using namespace std;
//head

#define maxn 20
int a[maxn] = { 0 };
int maxa = 0;
int ans = 0;
bool update(int ls, int rs)
{
	rep(i, ls + 1, rs + 1)
	{
		if(a[i] < a[i - 1]) return false;
	}
	return true;
}
void dfs(int ls, int rs)
{
	if(ls == rs) 
	{
		maxa = max(maxa, 1);
		return;
	}
	if(update(ls, rs)) maxa = max(maxa, rs - ls + 1);
	else
	{
		int mid = (ls + rs) / 2;
		dfs(ls, mid);
		dfs(mid + 1, rs);
	}

}

int main()
{
	int n;
	cin >> n;
	rep(i, 1, n + 1) scanf("%d", &a[i]);
	if(update(1, n)) return !printf("%d\n", n);
	dfs(1, n);
	printf("%d\n", maxa);
	return 0;
}