480 二叉树的所有路径

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: the root of the binary tree
     * @return: all root-to-leaf paths
     */
    vector<string> binaryTreePaths(TreeNode * root) {
        // write your code here
     vector<string> result;
     if (root==NULL)
     {
         return result;
     }
     string s="";
     int2str(root->val,s);
     if (root->left==NULL&&root->right==NULL)
     {
         result.push_back(s);
         return result;
     }
     if (root->left)
     {
         tra(result,s,root->left);
     }
     if (root->right)
     {
         tra(result,s,root->right);
     } 
     return result;
    }
    
    void tra(vector<string> &result,string s,TreeNode * root)//s不需要定义成引用类型，不需要保存其上一步结果，因为二叉树向下递归时s值自然累加节点值;
{
    string tmp;
    int2str(root->val,tmp);
    s=s+"->"+tmp;
    if (root->left==NULL&&root->right==NULL)
    {
        result.push_back(s);
        return ;
    }
    if (root->left)
    {
        tra(result,s,root->left);
    }
    if (root->right)
    {
        tra(result,s,root->right);
    }
    
}
    
    void int2str(const int &int_tmp,string &string_tmp)
{
    stringstream s;
    s<<int_tmp;
    string_tmp=s.str();//或者 s>>string_tmp;
}
};