Leetcode: Sum Root to Leaf Number

violet_program

于 2013-07-16 11:09:04 发布

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分类专栏： Recursive Tree Easy

本文链接：https://blog.youkuaiyun.com/violet_program/article/details/9340691

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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。通过递归遍历的方式，将每个路径上的节点值组合成完整的数字，并最终求得所有有效路径数字的总和。

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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
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int sumNumbers(TreeNode root) {
		// Start typing your Java solution below
		// DO NOT write main() function
		if(root == null)
			return 0;
		return calculate(root, 0);
	}
	
	public int calculate(TreeNode root, int temp){
		temp = temp * 10 + root.val;
		if(root.left == null && root.right == null)
			return temp;
		int left = 0, right = 0;
		if(root.left != null)
			left = calculate(root.left, temp);
		if(root.right != null)
			right = calculate(root.right, temp);
		return left + right;
	}
}