Leetcode 515. Find Largest Value in Each Tree Row

アプローチ

• DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public HashMap<Integer, Integer> hashMap;

    public List<Integer> largestValues(TreeNode root) {
        hashMap = new HashMap<>();
        dfs(root, Integer.MIN_VALUE, hashMap);
        return hashMap.values().stream().toList();
    }


    public void dfs(TreeNode root, int depth, HashMap<Integer, Integer> hashMap) {

        if (root == null) {
            return;
        }

        int val = hashMap.getOrDefault(depth, Integer.MIN_VALUE);

        if (val <= root.val) {
            hashMap.put(depth, root.val);
        }

        dfs(root.left, depth + 1, hashMap);
        dfs(root.right, depth + 1, hashMap);
    }
}