day18 - 二叉树 part05

zqh2023 / 2023-08-29 / 原文

513. 找树左下角的值

详解

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int max_depth = INT_MIN;
    void search(TreeNode* node, int depth, int& result){
        //前序遍历 中左右
        //父节点控制结束
        if(node->left == NULL && node->right == NULL){
            if(depth > max_depth){
                max_depth = depth;
                result = node->val;
            }
            return;
        }
        if(node->left){
            depth++;
            search(node->left, depth, result);
            depth--;//深度回溯
        }
        if(node->right){
            depth++;
            search(node->right, depth, result);
            depth--;//深度回溯
        }
        return;
    }

    int findBottomLeftValue_recursion(TreeNode* root) {
        int result;
        search(root, 0, result);
        return result;
    }

    int findBottomLeftValue(TreeNode* root) {
        int result;
        queue<TreeNode*> queue_1;
        if(!root) return 0;
        queue_1.push(root);
        while(!queue_1.empty()){
            int size = queue_1.size();//cout<<size<<endl;
            for(int i=0; i< size; i++){
                TreeNode* tmp = queue_1.front();
                if(i == 0)
                    result = tmp->val;
                queue_1.pop();
                if(tmp->left) queue_1.push(tmp->left);
                if(tmp->right) queue_1.push(tmp->right);
            }
            
        }
        return result;
    }
};