Binary Tree Longest Consecutive Sequence III

Posted 2020-09-21 codingEskimo

Note:

This question is good summary for this kind of problem. 
1) Once you get the root, loop through all the children. Get the max up/down/max from the children. 

2) set root max = up + down + 1, then comparing with the max got from the children. 

3) Return the max, current up and down. 

/**
 * Definition for a multi tree node.
 * public class MultiTreeNode {
 *     int val;
 *     List<TreeNode> children;
 *     MultiTreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    /**
     * @param root the root of k-ary tree
     * @return the length of the longest consecutive sequence path
     */
    private class ResultType {
        int max;
        int up;
        int down;
        public ResultType(int max, int up, int down) {
            this.max = max;
            this.up = up;
            this.down = down;
        }
    }
    public int longestConsecutive3(MultiTreeNode root) {
        // Write your code here
        return findLongestConsecutive(root).max;    
    }
    
    private ResultType findLongestConsecutive(MultiTreeNode root) {
        if (root == null) {
            return new ResultType(0, 0, 0);
        }
        
        int up = 0, down = 0, max = 1; //at least max could be 1;
        //In the loop, we need to get the max up, down, max from root‘s child
        for (MultiTreeNode child : root.children) {
            ResultType childRst = findLongestConsecutive(child);
            if (child != null && child.val + 1 == root.val) {
                down = Math.max(down, childRst.down + 1);
            }
            if (child != null && child.val - 1 == root.val) {
                up = Math.max(up, childRst.up + 1);
            }
            max = Math.max(max, childRst.max); // 
        }
        max = Math.max(up + down + 1, max);
        return new ResultType(max, up, down);
    }
    
    
}