c++ 二叉树打印节点路径
leetcode上有道题是关于path sum的，我第一时间的做法是用二叉树的路径去与sum比较。所以需要去打印出二叉树的节点路径，以下是用回溯法。
1 #include<iostream> 2 #include<vector> 3 using namespace std; 4 5 struct TreeNode { 6 int val; 7 TreeNode *left; 8 TreeNode *right; 9 TreeNode(int x) : val(x), left(NULL), right(NULL) {} 10 11 }; 12 class Solution { 13 public: 14 bool hasPathSum(TreeNode* root, int sum) { 15 vector<int> path; 16 path.reserve(100); 17 bool flag = false; 18 printPaths(root, path, 0); 19 return flag; 20 } 21 void printPaths(TreeNode* node, vector<int>& path, int pathlen) { 22 if (node == NULL) return; 23 // append this node to the path array 24 path[pathlen++] = node->val; 25 // path.push_back(node->val); 26 // it's a leaf, so print the path that led to here 27 if (node->left == NULL && node->right == NULL) { 28 printArray(path, pathlen); 29 } 30 else { 31 // otherwise try both subtrees 32 printPaths(node->left, path, pathlen); 33 printPaths(node->right, path, pathlen); 34 path.pop_back(); 35 } 36 } 37 void printArray(vector<int> &ints, int len) { 38 for (int i = 0; i < len; i++) { 39 cout << ints[i] << " " ; 40 } 41 cout << endl; 42 } 43 }; 44 45 int main() 46 { 47 Solution res; 48 TreeNode t1(5); 49 TreeNode t2(4); 50 TreeNode t3(8); 51 TreeNode t4(11); 52 TreeNode t5(13); 53 TreeNode t6(4); 54 TreeNode t7(7); 55 TreeNode t8(2); 56 TreeNode t9(1); 57 t1.left = &t2; 58 t1.right = &t3; 59 t2.left = &t4; 60 t3.left = &t5; 61 t3.right = &t6; 62 t4.left = &t7; 63 t4.right = &t8; 64 t6.right = &t9; 65 TreeNode * root = &t1; 66 bool ret = res.hasPathSum(root,22); 67 68 system("pause"); 69 return 0; 70 }
接着与sum做比较就能知道path sum是否相同了。
1 class Solution { 2 public: 3 bool hasPathSum(TreeNode* root, int sum) { 4 vector<int> path; 5 path.reserve(100); 6 bool flag = false; 7 printPaths(root, path, 0, sum, flag); 8 return flag; 9 } 10 void printPaths(TreeNode* node, vector<int>& path, int pathlen, int& sum, bool& flag) { 11 if (node == NULL) return; 12 // append this node to the path array 13 path[pathlen++] = node->val; 14 // path.push_back(node->val); 15 // it's a leaf, so print the path that led to here 16 if (node->left == NULL && node->right == NULL) { 17 printArray(path, pathlen, sum, flag); 18 if (flag) return; 19 } 20 else { 21 // otherwise try both subtrees 22 printPaths(node->left, path, pathlen, sum, flag); 23 printPaths(node->right, path, pathlen, sum, flag); 24 path.pop_back(); 25 } 26 } 27 void printArray(vector<int> &ints, int len, int& sum, bool& flag) { 28 int num = 0; 29 for (int i = 0; i < len; i++) { 30 // cout << ints[i] << " " ; 31 num += ints[i]; 32 } 33 if (num == sum) flag = true; 34 // cout << endl; 35 } 36 };
不过这种方法不好，空间开销大，效率还不高。在网上看到这种解法贴一下地址：
