【leetcode】129. Sum Root to Leaf Numbers【java】

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 a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
 //递归
public class Solution {
    public int sumNumbers(TreeNode root) {
         return helper(root, 0);
    }
    public int helper(TreeNode root, int curSum) {
        if (root == null) {
            return 0;
        }
        curSum = curSum * 10 + root.val;
        if (root.left == null && root.right ==null) {
            return curSum;
        }
        return helper(root.left, curSum) + helper(root.right, curSum);
    }
}

//非递归  DFS
public class Solution {
    public int sumNumbers(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int sum = 0;
        TreeNode curr;
        Stack stack = new Stack();
        stack.push(root);
        while (!stack.isEmpty()) {
            curr = stack.pop();
            if (curr.right != null) {
                curr.right.val = curr.val * 10 + curr.right.val;
                stack.push(curr.right);
            }
            if (curr.left != null) {
                curr.left.val = curr.val * 10 + curr.left.val;
                stack.push(curr.left);
            }
            if (curr.left == null && curr.right == null) {
                sum += curr.val;
            }
        }
        return sum;
    }
}