java 298.二叉树最长的连续序列（第1个）.java

Posted 2021-05-08

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    int maxLen = 0;
    public int longestConsecutive(TreeNode root) {
        int cur = opt(root);
        return Math.max(maxLen, cur); // [1]
    }
    
    private int opt(TreeNode root) {
        if(root == null) return 0;
        if(root.left == null && root.right == null) return 1;
        int left = opt(root.left);
        int right = opt(root.right);
        
        int res = 1;
        
        if(left > 0 && right > 0 && root.left.val - 1 == root.val && root.right.val - 1 == root.val) {
            res += Math.max(left, right);
        } else if (left > 0 && root.left.val - 1 == root.val) {
            res += left;
        } else if(right > 0 && root.right.val - 1 == root.val) {
            res += right;
        } 
        maxLen = Math.max(maxLen, res);
        return res;
    }
    
}

/*
*/

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int longestConsecutive(TreeNode root) {
        if(root == null) return 0;
        
        return longestConsecutive(root, root.val - 1, 0, 0);
    }
    public int longestConsecutive(TreeNode node, int prev, int sum, int maxsum){
        if(node == null) return Math.max(maxsum, sum);
        
        if(node.val == prev + 1){
            sum += 1;
        }else{
            sum = 1;
        }
        maxsum = Math.max(maxsum, sum);
        
        return Math.max(
            longestConsecutive(node.left,  node.val, sum, maxsum), 
            longestConsecutive(node.right, node.val, sum, maxsum));
    }
}