leetcode——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.

递归解法：

/**
 * Definition for a binary tree node.
 * 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);
	}
	int dfs(TreeNode* root,int sum)
	{
	     
         if(root == NULL) return 0;
         if(root->left == NULL && root->right == NULL) return root->val + sum * 10;         
         return dfs(root->left, root->val + sum * 10) + dfs(root->right, root->val + sum * 10); 

	}
	
};

非递归解法：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
	int sumNumbers(TreeNode* root) {
	    int sum = 0;
        if(root == NULL) 
            return sum;
        queue<TreeNode*> queue; 
        queue.push(root);
        while(!queue.empty()) {
            int levelLen = queue.size();            
            for (int i = 0; i < levelLen; i++) {
                TreeNode* node = queue.front();
                queue.pop();
                if(node->left == NULL && node->right == NULL)
                    sum += node->val;
                if(node->left != NULL) {
                    node->left->val += node->val * 10;
                    queue.push(node->left);
                }
                if(node->right != NULL) {
                    node->right->val += node->val * 10;
                    queue.push(node->right);
                }
            }
        }
        return sum;
    }
	
};