129. Sum Root to Leaf Numbers.md

129. Sum Root to Leaf Numbers

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.

Note: A leaf is a node with no children.

Example:

Input: [1,2,3]
    1
   / \
  2   3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.

Example 2:

Input: [4,9,0,5,1]
    4
   / \
  9   0
 / \
5   1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.

Solution

递归太好用了，over

Code

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

def rootsum(root,value,res):
    if root is None:
        return res
    
    if root.left is None and root.right is None:
        res += value*10+root.val

    else:
        res = rootsum(root.left,value*10+root.val,res)
        res = rootsum(root.right,value*10+root.val,res)
        
    return res
    
    
class Solution(object):
    def sumNumbers(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        res = 0
        value = 0
        res = rootsum(root,value,res)
        return res

Code2 - java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int result = 0;
    private void helper(TreeNode root, int path)
    {
        if(root == null)
            return;
        if(root.left == null && root.right == null)
        {
            path = path * 10 + root.val;
            result += path;
        }
        if(root.left != null)
            helper(root.left,path*10+root.val);
        if(root.right != null)
            helper(root.right, path*10+root.val);
            
    }
    public int sumNumbers(TreeNode root) {
        int path = 0;
        helper(root,path);
        return result;
        
        
    }
}