Li Kou daily question leetcode 513. find the value in the lower left corner of the tree

leetcode 513. Find the value in the lower left corner of the tree

Ideas Simple depth traversal , It combines the idea of post order traversal of binary tree . First, keep walking down , When traversing downward, first traverse left （ Ensure that the deepest value obtained is on the far left ）, If you find that the traversal depth is greater than the existing depth, change the maximum depth to the current depth , Values are also modified .

class Solution {
    
    int val;
    int deep = -1;
    public void dfs(TreeNode root,int depth){
    
        if(root == null)return;

        dfs(root.left,depth+1);// Traverse left 
        dfs(root.right,depth+1);// Traverse right 

        if(depth > deep){
    // When the code runs here, all the child nodes of this node have been traversed , If you don't understand, you can look at the post order traversal of binary trees , The core is backtracking 
            deep = depth;// Modify depth 
            val = root.val;// Modified value 
        }
    }

    public int findBottomLeftValue(TreeNode root) {
    
        dfs(root,0);
        return val;
    }
}