Sum Root to Leaf Numbers

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本文介绍了一种算法，用于计算给定二叉树中所有从根节点到叶子节点的路径所代表数字的总和。通过递归遍历的方式，实现了对二叉树的有效处理，并给出了具体的实现代码。

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 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;
        if(isLeaf(root)) return root.val;
        return leafNum(root,root.val);
    }
    public int leafNum(TreeNode node,int n){
        if(isLeaf(node)){
            return n;
        } 
        int l=0,r=0;
        if(node.left!=null){
            int m=10*n+(node.left.val);
            l= leafNum(node.left,m);
        } 
        if(node.right!=null){
            int m=10*n+(node.right.val);
            r=leafNum(node.right,m);
        }
        return l+r;
    }
    public boolean isLeaf(TreeNode node){
        if(node.left==null && node.right==null) return true;
        else return false;
    }
}