679. 24 点游戏

679. 24 点游戏

---

题目链接：679. 24 点游戏

代码如下：

//参考链接：https://leetcode.cn/problems/24-game/solutions/3756006/mei-ci-he-bing-liang-zhang-pai-di-gui-xi-0sdu
class Solution {
public:
	bool judgePoint24(vector<int>& cards) {
		vector<double> a(cards.begin(),cards.end());
		return dfs(a);
	}

private:
	const double EPS = 1e-9;
	
	bool dfs(vector<double>& cards) {
		int n = cards.size();
		if (n == 1) {
			return abs(cards[0] - 24) < EPS; // 如果只剩一个数，判断是否接近 24
		}

		//选两张牌 x=cartds[i]和y=cards[j]，进行四则运算
		for (int i = 0;i < n;i++) {
			double x = cards[i];
			for (int j = i + 1;j < n;j++) {
				double y = cards[j];
			
				//六种情况：加减乘除，其中减和除都有两种不同的顺序
				vector<double> candidates = { x + y,x - y,y - x,x * y };
				if (abs(y) > EPS) {
					candidates.push_back(x / y);
				}
				if (abs(x) > EPS) {
					candidates.push_back(y / x);
				}

				auto new_cards = cards;
				new_cards.erase(new_cards.begin() + j); // 移除第 j 张牌
				for (double res : candidates) {
					new_cards[i] = res; // 将结果放在第 i 张牌的位置
					if (dfs(new_cards)) {
						return true;
					}
				}
			}
		}
		return false; // 如果没有找到满足条件的组合，返回 false
	}
};