[LeetCode130]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.

Analysis:

Once we see this kind of problem, no matter what sum is required to output, "all root-to-leaf" phrase reminds us the classic Tree Traversal or Depth-First-Search algorithm. Then according to the specific problem, compute and store the values we need. Here in this problem, while searching deeper, add the values up (times 10 + current value), and add the sum to final result if meet the leaf node (left and right child are both NULL).

Java

public class Solution {    int result;public int sumNumbers(TreeNode root) {        result = 0;        getSum(root, 0);        return result;    }public void getSum(TreeNode root, int path){if(root==null) return;path = path*10+root.val;if(root.left==null && root.right==null){result+=path;return;}getSum(root.left, path);getSum(root.right, path);}}

c++

void sumSubpath(TreeNode* root, int &sum, int path){    if(root == NULL) return;    path = path*10 + root->val;    if(root->left == NULL && root->right == NULL){        sum += path;        return;    }    sumSubpath(root->left, sum, path);    sumSubpath(root->right, sum, path);}int sumNumbers(TreeNode *root) {    int sum = 0;    int path = 0;    sumSubpath(root,sum,0);    return sum;}