leetcode-sum root to leaf numbers
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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
.
public class Solution { int result=0; public int sumNumbers(TreeNode root) { if(root==null)return result; mySum(root,0); return result; } public void mySum(TreeNode root,int value){ int cur=10*value+root.val; if(root.left==null&&root.right==null)result+=cur; if(root.right!=null)mySum(root.right,cur); if(root.left!=null)mySum(root.left,cur); }}树的问题很多都是层遍历,由上到下,由下到上。由下到上的就要在上面接受下面返回来的数值,由上到下就简单一些,数值一步一步传下去,然后在最底层判断结束条件做相应的处理。
这道题目需要用由上到下的想法,因为涉及到一个值传递到两个分支中,同时需要对层数有所了解。
需要注意的是结束条件:
当左子树和右子树都是null的时候才能加入这个值。
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