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
.
解題思路:
1,樹中有3類結點:孩子結點,中間節點,空結點
2,對於不同的結點類型返回不同的值;
如果是空節點,返回0;如果是中間節點,返回左右子樹的計算和;如果是孩子節點,返回當前計算和*10加上孩子節點的值;
由此遞歸計算出所有分支的和。
AC代碼:
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumNumbers(TreeNode *root) {
if(root == NULL) return 0;
else if(root->left == NULL && root->right == NULL) return root->val;
int sum = 0;
sum = add(root,0);
return sum;
}
private:
int add(TreeNode *node,int curSum){
//如果是空結點,返回0
if(node == NULL) return 0;
//如果是葉子結點,返回當前值的和加上葉子結點的值
else if(node->left == NULL && node->right == NULL){
return curSum * 10 + node->val;
}
//如果是中間節點,返回左右節點的和
else{
return add(node->left,curSum * 10 + node->val) + add(node->right,curSum * 10 + node->val);
}
}
};