Leetcode之深度优先搜索（DFS）专题-513. 找树左下角的值（Find Bottom Left Tree Value）

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    List<List<Integer>> ans = new ArrayList<>();
    public int findBottomLeftValue(TreeNode root) {
        dfs(root,0);
        return ans.get(ans.size()-1).get(0);
    }
    public void dfs(TreeNode node,int depth){
        if(node==null) return;
        
        if(ans.size()==depth){
            ans.add(new ArrayList<Integer>());
        }
        
        ans.get(depth).add(node.val);
        dfs(node.left,depth+1);
        dfs(node.right,depth+1);
    }
}