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LeetCode: Sum Root to Leaf Numbers 解题报告
Sum Root to Leaf Numbers
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.
SOLUTION 1:
使用递归完成。我们要做的是 把左右子树的path加起来。
base case: root是叶子节点时,直接计算path。我们用pre保留上一层计算出来的数字的值。那么到了当前根节点应该就是
把上一层的值*10再加上root的值。
1 /** 2 * Definition for binary tree 3 * public class TreeNode { 4 * int val; 5 * TreeNode left; 6 * TreeNode right; 7 * TreeNode(int x) { val = x; } 8 * } 9 */10 public class Solution {11 public int sumNumbers(TreeNode root) {12 return dfs(root, 0);13 }14 15 public int dfs(TreeNode root, int pre) {16 if (root == null) {17 return 0;18 }19 20 int cur = pre * 10 + root.val;21 if (root.left == null && root.right == null) {22 return cur;23 }24 25 return dfs(root.left, cur) + dfs(root.right, cur);26 }27 }
GITHUB:
https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/tree/SumNumbers_1208_2014.java
LeetCode: Sum Root to Leaf Numbers 解题报告
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