leetcode 86: Sum Root to Leaf Numbers

Sum Root to Leaf Numbers2 days

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

An example is the root-to-leaf path 1->2->3 which represents the number 123.

Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.

Return the sum = 12 + 13 = 25.

wrong try. bottom up. should use top bottom

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
       if(root==null) return 0; 
       Pair pair = sumRec( root);
       
       return pair.first;
    }
    
    private Pair sumRec(TreeNode root) {
        if(root==null) {
            return new Pair(-1,0);
        }
        
        Pair left = sumRec(root.left);
        Pair right = sumRec(root.right);
        int x = root.val;
        
        int l = 0, r=0;
        if(left.first!=-1) {
             l = (int)(root.val * Math.pow(10,left.second)) + left.first;
        } else {
             l = 0;
        }
        
        if(right.first !=-1) {
            r = (int)(root.val * Math.pow(10,right.second)) + right.first;
        } else {
            r = 0;
        }
        
        return new Pair( l+r, (left.second>right.second ? left.second+1 : right.second+1) );
    }
    
    static class Pair{
        public int first;
        public int second;
        public Pair(int x, int y) {first=x; second=y;} 
        
    }
}

correct one:

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        return sumRec(root, 0);
    }
    
    private int sumRec(TreeNode root, int num) {
        if(root==null) {
            return 0;
        }
        
        num = num*10 + root.val;
    
        int left=0, right=0;
        if(root.left!=null) left = sumRec(root.left, num);
        if(root.right!=null) right = sumRec(root.right, num);
        
        int res = left + right;
        return res==0? num : res;    
    }
}

final version:

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
        // Start typing your Java solution below
        // DO NOT write main() function
        
        if(root==null) return 0;
        return  sumRec(root, 0) ;
    }
    
    private int sumRec(TreeNode root, int parentSum) {
        
        int x = parentSum*10 + root.val;
        
        int l=0, r=0;
        
        if(root.left!=null) {
            l = sumRec(root.left, x);
        }
        
        if(root.right!=null) {   
            r = sumRec(root.right, x);
        }
        
        if( l==0 && r==0) return x;
        else return l+r;
    }
}