Sum Root to Leaf Numbers - LeetCode

最新推荐文章于 2022-03-02 22:54:17 发布

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本文探讨了如何计算给定二叉树中从根节点到每个叶子节点路径所代表的数字之和。通过遍历树结构并累积路径上的数值，最终得出总和为25的实例，展示了算法实现过程。

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.

不要搞错叶子的判断条件，

if(root.left == null && root.right == null)

以下是AC代码：

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
   	private ArrayList<String> result = new ArrayList<String>();
	private String r = new String("");
	private int sum = 0;
	public void sumHelper(TreeNode root){
		if(root.left == null && root.right == null){
			sum = sum + Integer.valueOf(r + root.val);
			return;
		}
		else{
			int l = r.length();
			r = r + root.val;
			if(root.left != null)
			sumHelper(root.left);
			if(root.right != null)
			sumHelper(root.right);
			r = r.substring(0, l);
			return;
		}
	}
	 public int sumNumbers(TreeNode root) {
	        if(root == null)
	        	return 0;
	        else
	        {
	        	sumHelper(root);
	        	return sum;
	        }
	    }
}