找到所有根到叶子的路径
深度优先搜索（DFS）， 即二叉树的先序遍历。
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 class Solution { 11 public: 12 vector<string> vs_; 13 void dfs(TreeNode* root, string s){ 14 if(!root) return; 15 if(!root->left && !root->right){ 16 char t[20] = ""; 17 sprintf(t, "->%d", root->val); 18 vs_.push_back(s + string(t)); 19 return; 20 } 21 else{ 22 char t[20] = ""; 23 sprintf(t, "->%d", root->val); 24 dfs(root->left, s + string(t)); 25 dfs(root->right, s + string(t)); 26 } 27 } 28 vector<string> binaryTreePaths(TreeNode* root) { 29 vs_.clear(); 30 if(!root) return vs_; 31 char t[20] = ""; 32 sprintf(t, "%d", root->val); 33 string s(t); 34 if(!root->left && !root->right){ 35 vs_.push_back(s); 36 return vs_; 37 } 38 dfs(root->left, s); 39 dfs(root->right, s); 40 return vs_; 41 } 42 };