[leetcode][tree] Binary Tree Paths

题目：

Given a binary tree, return all root-to-leaf paths.

For example, given the following binary tree:

1
/   \
2     3
\
5

All root-to-leaf paths are:

["1->2->5", "1->3"]

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
#include <stdlib.h>
class Solution {
public:
vector<string> binaryTreePaths(TreeNode* root) {
vector<string> res;
if(root == NULL) return res;
string onePath;
binaryTreePathsCore(root, onePath, res);
return res;
}
private:
char *itoa(int x, char *str){
if(x == 0){
str[0] = '0';
str[1] = '\0';
return str;
}
int i = 0;
if(x < 0){
x = -x;
str[i++] = '-';
}
int start = i;
while(x > 0){
str[i++] = x%10+'0';
x /= 10;
}
str[i] = '\0';
reverse(str+start, str+i);
return str;
}
void binaryTreePathsCore(TreeNode *root, string onePath, vector<string> &res){
if(root == NULL) return;
char str[12];
itoa(root->val, str);
onePath += str;
if(root->left == NULL && root->right == NULL){
res.push_back(onePath);
return;
}
onePath += "->";
if(root->left != NULL) binaryTreePathsCore(root->left, onePath, res);
if(root->right != NULL) binaryTreePathsCore(root->right, onePath, res);
}
};