[298. Binary Tree Longest Consecutive Sequence] #leetcode

298_0903.java

class Solution {
  // O(n) o(h)
    private int max = 0;
    public int longestConsecutive(TreeNode root) {
        if (root == null) return 0;
        
        dfs(root, 0, root.val);
        return max;
    }
    
    private void dfs(TreeNode node, int cur, int target) {
        if (node == null) return;
        if (node.val == target) cur++;
        else cur = 1;
        max = Math.max(cur, max);
        
        dfs(node.left, cur, node.val+1);
        dfs(node.right, cur, node.val+1);
    }
}