【Leetcode】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.

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.

Java:

这题就是注意边界的取值就行了，

/**
 * 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) {
        return help(root,0);
    }
    private int help(TreeNode node, int sum)
    {
        if(node==null)     return 0;
        sum=sum*10+node.val;
        if(node.left==null&&node.right==null) return sum;//只有在左右没有子树的的情况才能返回
        return help(node.left, sum)+help(node.right, sum);
    }
}

征服： Sum Root to Leaf Numbers -- LeetCode

public int sumNumbers(TreeNode root) {  
    return helper(root,0);  
}  
private int helper(TreeNode root, int sum)  
{  
    if(root == null)  
        return 0;  
    if(root.left==null && root.right==null)  
        return sum*10+root.val;  
    return helper(root.left,sum*10+root.val)+helper(root.right,sum*10+root.val);  
}  

2.伪技回忆录： Sum Root to leaf Numbers

public class Solution {  
    public int sumNumbers(TreeNode root) {  
        if(root == null) return 0;  
        return helper(root, 0, 0);  
    }  
    public int helper(TreeNode node, int num, int sum){  
        if(node == null) return sum;           
        num = num*10 + node.val;  
        // leaf reached  
        if(node.left == null && node.right == null) {  
            sum += num;  
            return sum;  
        }  
        // sum of left subtree + right subtree  
        sum = helper(node.left, num, sum) + helper(node.right, num, sum);  
        return sum;  
    }  
}