LeetCode Sum Root to Leaf Numbers

coobj2008

于 2014-03-21 22:35:59 发布

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CC 4.0 BY-SA版权

本文链接：https://blog.youkuaiyun.com/coobj2008/article/details/21748017

本文介绍了一种算法，用于计算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。通过深度优先搜索的方式遍历二叉树，并累加每个路径上的数字。

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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.

/**
 * 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) {
    	if(root == NULL)
    		return 0;
    	return dfs(root, 0);
        
    }
    //自顶向下 
    int dfs(TreeNode *root, int pre) {
    	int sum = pre * 10 + root->val;
    	if(root->left == NULL && root->right == NULL)
    		return sum;
    	if(root->right == NULL)
    		return dfs(root->left, sum);
    	if(root->left == NULL)
    		return dfs(root->right, sum);
    	return dfs(root->left, sum) + dfs(root->right, sum);
    }
};