129. Sum Root to Leaf Numbers

最新推荐文章于 2020-10-29 09:30:55 发布

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本文介绍了一种解决特定二叉树问题的方法：计算所有从根节点到叶子节点的路径数值之和。通过深度优先搜索(DFS)遍历二叉树，并采用递归算法来实现这一目标。

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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.

DFS

public class Solution {
    public int sumNumbers(TreeNode root) {
       return helper(root,0);
    }
    public int helper(TreeNode root,int count){
        if(root==null) return 0;
        if(root.left==null&&root.right==null)  return count*10+root.val;
        return helper(root.left,count*10+root.val)+helper(root.right,count*10+root.val);
    }
}