Sum Root to Leaf Numbers

cfcf0517

于 2015-08-08 20:33:40 发布

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分类专栏： LeetCode java

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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。通过递归深度优先搜索的方法，实现了对二叉树的有效遍历。

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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.

使用递归实现深度搜索

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