题目

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.

解答

用树的递归解决

/**

 * 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) {

        if(root==null){

            return 0;

        }

        return sum(root,0);

    }

    public int sum(TreeNode node,int parentVal){

        int sum=0;

        int temp=parentVal*10+node.val;

        if(node.left==null&&node.right==null){

            sum=temp;

        }

        if(node.left!=null){

            sum+=sum(node.left,temp);

        }

        if(node.right!=null){

            sum+=sum(node.right,temp);

        }

        return sum;

    }

} 

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