題目:
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
.
題解:
分析這道題,由根節點往葉節點方向走,就是從高位往地位加和的方向。也就是說,當遍歷的節點往葉節點方向走一層的時候,該節點的值應為父節點的值*10+當前節點的值。
由此可以寫出程式碼:
1 int sumhelper(TreeNode root, int levelBase) {
2 if(root == null)
3 return 0;
4
5 if(root.left == null && root.right == null) {
6 return levelBase + root.val;
7 }
8
9 int nextLevelBase = (levelBase + root.val)*10 ;
10 int leftSubTreeSum = sumhelper(root.left, nextLevelBase);
11 int rightSubTreeSum = sumhelper(root.right, nextLevelBase);
12
13 return leftSubTreeSum + rightSubTreeSum;
14 }
15
16 public int sumNumbers(TreeNode root) {
17 return sumhelper(root,0);
18 }
2 if(root == null)
3 return 0;
4
5 if(root.left == null && root.right == null) {
6 return levelBase + root.val;
7 }
8
9 int nextLevelBase = (levelBase + root.val)*10 ;
10 int leftSubTreeSum = sumhelper(root.left, nextLevelBase);
11 int rightSubTreeSum = sumhelper(root.right, nextLevelBase);
12
13 return leftSubTreeSum + rightSubTreeSum;
14 }
15
16 public int sumNumbers(TreeNode root) {
17 return sumhelper(root,0);
18 }