[leedcode 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.

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.

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    //从根节点到叶子节点的路径代表一个数值，找出所有的这些数值然后累加得到一个和。DFS
    //本题主要注意getRes函数的参数，path代表到达node节点时，路径上已经存在的和！
    //本题注意题意：只有到达叶子节点（left=right=null）才能够将结果保存到res，所以注意递归结束条件
    int res;
    public int sumNumbers(TreeNode root) {
        getRes(root,0);
        return res;
        
    }
    public void getRes(TreeNode node,int path){//注意path参数含义！
        if(node==null) return;
        int temp=path*10+node.val;
        if(node.left==null&&node.right==null){
            res+=temp;
            return;
        }
        getRes(node.left,temp);
        getRes(node.right,temp);
        
    }
}