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给定仅包含来自0-9
的数字的二叉树,每个根到叶路径可以表示数字。举个例子:root-to-leaf路径1-> 2-> 3
,它代表数字123
,找到所有根到叶的数的总和
样例
Example:
Input: [1,2,3]
1
/ \
2 3
Output: 25
Explanation:
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Therefore, sum = 12 + 13 = 25.
Example 2:
Input: [4,9,0,5,1]
4
/ \
9 0
/ \
5 1
Output: 1026
Explanation:
The root-to-leaf path 4->9->5 represents the number 495.
The root-to-leaf path 4->9->1 represents the number 491.
The root-to-leaf path 4->0 represents the number 40.
Therefore, sum = 495 + 491 + 40 = 1026.
注意事项
叶节点是没有子节点的节点
解题思路:
DFS.
/**
* Definition of TreeNode:
* public class TreeNode {
* public int val;
* public TreeNode left, right;
* public TreeNode(int val) {
* this.val = val;
* this.left = this.right = null;
* }
* }
*/
public class Solution {
/**
* @param root: the root of the tree
* @return: the total sum of all root-to-leaf numbers
*/
public int sumNumbers(TreeNode root) {
// write your code here
return dfs(root, 0);
}
private int dfs(TreeNode root, int prev){
if(root == null)
return 0;
int sum = root.val + prev * 10;
if(root.left == null && root.right == null) {
return sum;
}
return dfs(root.left, sum) + dfs(root.right, sum);
}
}