代码随想录Day16

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LeetCode513.找树左下角的值

class Solution {
public:
    int maxDepth = INT_MIN;
    int result;
    void dfs(TreeNode* root, int depth){
        if(root->left == nullptr && root->right == nullptr){
            if(depth > maxDepth){
                maxDepth = depth;
                result = root->val;
                return;
            }
        }
        if(root->left){
            dfs(root->left, depth + 1);
        }
        if(root->right){
            dfs(root->right, depth + 1);
        }
        return;
    }
    int findBottomLeftValue(TreeNode* root) {
        dfs(root, 0);
        return result;
    }
};

LeetCode112.路径总和

class Solution {
public:
    bool hasPathSum(TreeNode* root, int targetSum) {
        if(root == nullptr)return false;
        if(root->left == nullptr && root->right == nullptr){
            if(root->val == targetSum){
                return true;
            }
        }
        return hasPathSum(root->left, targetSum - root->val)||hasPathSum(root->right, targetSum - root->val);
    }
};

LeetCode106.从中序与后续遍历构建二叉树

class Solution {
public:
    TreeNode* buildTree(vector<int>& inorder, vector<int>& postorder) {
        if (postorder.size() == 0) return NULL;
        int delimeterIndex;
        int val;
        for(int i = 0; i < inorder.size();i++){
            if(inorder[i] == postorder[postorder.size() - 1]){
                delimeterIndex = i;
                val = inorder[i];
                break;
            }
        }
        TreeNode* root = new TreeNode(val);

        vector<int> inorderLeft(inorder.begin(), inorder.begin() + delimeterIndex);
        vector<int> inorderRight(inorder.begin() + delimeterIndex + 1, inorder.end());

        postorder.pop_back();
        vector<int> postorderLeft(postorder.begin(), postorder.begin() + delimeterIndex);
        vector<int> postorderRight(postorder.begin() + delimeterIndex, postorder.end());

        root->left = buildTree(inorderLeft, postorderLeft);
        root->right = buildTree(inorderRight, postorderRight);

        return root;
    }
};