[LeetCode] Sum Root to Leaf Numbers

题目：

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

.

解答：

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
private:
int TotalSum = 0;

public:
int sumNumbers(TreeNode *root) {
dfs(root, 0);
return TotalSum;
}

void dfs(TreeNode *root, int curSum) {
if(root == NULL) {
return;
}
if(root -> left == NULL && root -> right == NULL) {
curSum = curSum * 10 + root -> val;
TotalSum += curSum;
return;
}
curSum = curSum * 10 + root -> val;
dfs(root -> left, curSum);
dfs(root -> right, curSum);
return;
}
};

思路：

方法dfs负责深搜，到达叶子节点时记录局部和，再加到总和上；深搜方法设置一个当前和参数，负责记录深搜到左右孩子父节点时的和。