标签：style http color os io ar for div sp
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.
题意：给定一棵二叉树，每个节目包含数字0-9，根到叶子节点组成一个数字，
求所有这些数字的总和
思路：dfs
int sum
void dfs(TreeNode *root, int num)
num表示从根节点到当前节点前面的节点组成数字
这个函数求出，在num的基础上，从root 为根到它的所有叶子节点组成的数字的总和
复杂度：时间 O(n) ；空间 O(log n)
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumNumbers(TreeNode *root){
return dfs(root, 0);
}
private:
int dfs(TreeNode *root, int num){
if(!root) {return 0;} //空
if(!root->left && !root->right) {return num * 10 + root->val;} //叶子节点
return dfs(root->left, num * 10 + root->val) + dfs(root->right, num * 10 + root->val);
}
};Leetcode dfs Sum Root to Leaf Numbers
标签：style http color os io ar for div sp
原文地址：http://blog.csdn.net/zhengsenlie/article/details/39081635
