Datawhale-LeetCode编程实践组队学习Task09

88. 合并两个有序数组

class Solution {
public:
    void merge(vector<int>& nums1, int m, vector<int>& nums2, int n) {
        for (int i = 0; i != n; ++i) {
            nums1[m + i] = nums2[i];
        }
        sort(nums1.begin(), nums1.end());
    }
};

89. 格雷编码

class Solution1 {
public:
    vector<int> grayCode(int n) {
        vector<int> res;
        res.push_back(0);
        unordered_set<int> st;
        st.insert(0);
        int N = pow(2, n);
        dfs(n, N, res, st);
        return res;
    }

private:
    bool dfs(int n, int N, vector<int>& res, unordered_set<int>& st) {
        if (res.size() == N) {
            return true;
        }

        auto last = res.back();
        for (int i = 0; i < n; i++) {
            auto next = last;
            next ^= (0x1 << i);
            if (st.count(next)) {
                continue;
            }
            res.push_back(next);
            st.insert(next);
            if (dfs(n, N, res, st)) {
                return true;
            }
            res.pop_back();
            st.erase(next);
        }

        return false;
    }

};

// Binary code to gray code has a conversion formula
class Solution2 {
public:
    vector<int> grayCode(int n) {
        vector<int> res;
        int N = pow(2, n);
        for (int i = 0; i < N; i++) {
            res.push_back((i >> 1) ^ i);
        }

        return res;
    }

};

104. 二叉树的最大深度

class Solution {
public:
    int maxDepth(TreeNode* root) {
        if (root == nullptr) return 0;
        queue<TreeNode*> Q;
        Q.push(root);
        int ans = 0;
        while (!Q.empty()) {
            int sz = Q.size();
            while (sz > 0) {
                TreeNode* node = Q.front();Q.pop();
                if (node->left) Q.push(node->left);
                if (node->right) Q.push(node->right);
                sz -= 1;
            }
            ans += 1;
        } 
        return ans;
    }
};