《Cracking the Coding Interview》——第4章：树和图——题目4

2014-03-19 03:40

题目：给定一棵二叉树，把每一层的节点串成一个链表，最终返回一个链表数组。

解法：前序遍历，遍历的同时向各个链表里添加节点。水平遍历好像还不如前序遍历来得方便。

代码：

  1 // 4.4 Level order traversal
  2 #include <cstdio>
  3 #include <vector>
  4 using namespace std;
  5 
  6 struct TreeNode {
  7     int val;
  8     TreeNode *left;
  9     TreeNode *right;
 10     
 11     TreeNode(int _val = 0): val(_val), left(nullptr), right(nullptr) {};
 12 };
 13 
 14 struct ListNode {
 15     int val;
 16     ListNode *next;
 17     
 18     ListNode(int _val = 0): val(_val), next(nullptr) {};
 19 };
 20 
 21 void consructBSTFromSortedArray(vector<int> &v, int left, int right, TreeNode *&root)
 22 {
 23     if (left > right) {
 24         root = nullptr;
 25     } else {
 26         int mid = (left + right + 1) / 2;
 27         root = new TreeNode(v[mid]);
 28         consructBSTFromSortedArray(v, left, mid - 1, root->left);
 29         consructBSTFromSortedArray(v, mid + 1, right, root->right);
 30     }
 31 }
 32 
 33 void preorderTraversal(TreeNode *root, vector<ListNode *> &listHeads, vector<ListNode *> &listTails, int depth)
 34 {
 35     if (root == nullptr) {
 36         printf("# ");
 37     } else {
 38         while ((int)listHeads.size() < depth) {
 39             listHeads.push_back(nullptr);
 40             listTails.push_back(nullptr);
 41         }
 42         
 43         if (listHeads[depth - 1] == nullptr) {
 44             listHeads[depth - 1] = listTails[depth - 1] = new ListNode(root->val);
 45         } else {
 46             listTails[depth - 1]->next = new ListNode(root->val);
 47             listTails[depth - 1] = listTails[depth - 1]->next;
 48         }
 49         
 50         printf("%d ", root->val);
 51         preorderTraversal(root->left, listHeads, listTails, depth + 1);
 52         preorderTraversal(root->right, listHeads, listTails, depth + 1);
 53     }
 54 }
 55 
 56 void clearBinaryTree(TreeNode *&root)
 57 {
 58     if (root == nullptr) {
 59         return;
 60     } else {
 61         clearBinaryTree(root->left);
 62         clearBinaryTree(root->right);
 63         delete root;
 64         root = nullptr;
 65     }
 66 }
 67 
 68 void clearList(ListNode *&root)
 69 {
 70     ListNode *ptr;
 71     
 72     ptr = root;
 73     while (ptr != nullptr) {
 74         root = root->next;
 75         delete ptr;
 76         ptr = root;
 77     }
 78     root = nullptr;
 79 }
 80 
 81 int main()
 82 {
 83     TreeNode *root;
 84     int i, n;
 85     vector<int> v;
 86     vector<ListNode *> listHeads, listTails;
 87     ListNode *ptr;
 88     
 89     while (scanf("%d", &n) == 1 && n > 0) {
 90         for (i = 0; i < n; ++i) {
 91             v.push_back(i + 1);
 92         }
 93         
 94         consructBSTFromSortedArray(v, 0, n - 1, root);
 95         preorderTraversal(root, listHeads, listTails, 1);
 96         printf("\n");
 97         
 98         for (i = 0; i < (int)listHeads.size(); ++i) {
 99             printf("Level %d:", i + 1);
100             ptr = listHeads[i];
101             while (ptr != nullptr) {
102                 printf(" %d", ptr->val);
103                 ptr = ptr->next;
104             }
105             printf("\n");
106             clearList(listHeads[i]);
107         }
108         
109         v.clear();
110         clearBinaryTree(root);
111         listHeads.clear();
112         listTails.clear();
113     }
114     
115     return 0;
116 }

 

 posted on 2014-03-19 03:43  zhuli19901106  阅读(244)  评论(0)  编辑  收藏  举报