257. Binary Tree Paths

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 static int wing=[]()
11 {
12     std::ios::sync_with_stdio(false);
13     cin.tie(NULL);
14     return 0;
15 }();
16 
17 class Solution 
18 {
19 public:
20     vector<string> binaryTreePaths(TreeNode* root) 
21     {
22         vector<string> res;
23         TreeNode *p=root,*r=NULL;
24         stack<TreeNode*> s,h;
25         while(p||!s.empty())
26         {
27             if(p)
28             {
29                 s.push(p);
30                 p=p->left;
31             }
32             else
33             {
34                 p=s.top();
35                 if(p->right&&p->right!=r)
36                 {
37                     p=p->right;
38                     s.push(p);
39                     p=p->left;
40                 }
41                 else
42                 {
43                     if(p->left==NULL&&p->right==NULL)
44                     {
45                         h=s;
46                         string cur;
47                         int sz=h.size();
48                         while(sz>1)
49                         {
50                             TreeNode *ps=h.top();
51                             int value=ps->val;
52                             cur="->"+to_string(value)+cur;
53                             sz--;
54                             h.pop();
55                         }
56                         TreeNode *last=h.top();
57                         int lastvalue=last->val;
58                         cur=to_string(lastvalue)+cur;
59                         res.push_back(cur);
60                     }
61                     s.pop();
62                     r=p;
63                     p=NULL;
64                 }
65             }
66         }
67         return res;
68     }
69 };

利用后序遍历，在出栈访问节点时判定节点是否为叶节点，若是叶节点，就生成字符串并添加至结果中。