ちきんの括弧並べsolution of Kuske.cpp

#define _CRT_SECURE_NO_WARNINGS

#include <stdio.h>
#include <algorithm>
#include <iostream>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <vector>
#include <queue>
#include <functional>
#include <math.h>
#include <string.h>

using std::endl;
using std::string;

#define ll long long int
#define LEP(a, n) for(ll a = 0; a < n; ++a)
#define INF 123456789012345
#define OUT std::cout
#define IN std::cin
#define itn int
#define fro for
#define sdt std

ll N;

ll recurse(ll state, ll length, ll startN) {
	if (length == 0 && state == 0) return 1;
	if (length == 0 && state != 0) return 0;
	if (state < 0) return 0;
	if (startN > 0) return recurse(state + 1, length - 1, startN - 1) + recurse(state - 1, length - 1, startN);
	else if (state - length == 0) return 1;
	else return 0;
}

int main() {
	IN >> N;
	OUT << recurse(0, N * 2, N) << endl;

	return 0;
}