[leetcode]129. Sum Root to Leaf Numbers@Java解题报告

https://leetcode.com/problems/sum-root-to-leaf-numbers/description/

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.

package go.jacob.day810;

/**
 * 129. Sum Root to Leaf Numbers
 * 
 * @author Jacob
 *
 */
public class Demo1 {
	public int sumNumbers(TreeNode root) {
		if (root == null)
			return 0;
		int sum = 0;
		return sumNumbers(root, sum);
	}

	private int sumNumbers(TreeNode root, int sum) {
		if (root == null)
			return 0;
		if (root.left == null && root.right == null)
			return sum * 10 + root.val;
		return sumNumbers(root.left, 10 * sum + root.val) + 
				sumNumbers(root.right, 10 * sum + root.val);

	}
	/*
	 * My Solution
	 */
	private int sumNumbers_1(TreeNode root, int sum) {
		sum += root.val;
		int leftSum = 0;
		int rightSum = 0;
		if (root.left != null)
			leftSum = sumNumbers(root.left, 10 * (sum));
		if (root.right != null)
			rightSum = sumNumbers(root.right, 10 * (sum));
		// 如果root的左右子树为空，返回sum。否则返回左右子树递归的结果和
		return root.left == null && root.right == null ? sum : leftSum + rightSum;

	}
}