1066. Root of AVL Tree (25)【AVL树】——PAT (Advanced Level) Practise
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题目信息
1066. Root of AVL Tree (25)
时间限制100 ms
内存限制65536 kB
代码长度限制16000 B
An AVL tree is a self-balancing binary search tree. In an AVL tree, the heights of the two child subtrees of any node differ by at most one; if at any time they differ by more than one, rebalancing is done to restore this property. Figures 1-4 illustrate the rotation rules.
Now given a sequence of insertions, you are supposed to tell the root of the resulting AVL tree.
Input Specification:
Each input file contains one test case. For each case, the first line contains a positive integer N (<=20) which is the total number of keys to be inserted. Then N distinct integer keys are given in the next line. All the numbers in a line are separated by a space.
Output Specification:
For each test case, print ythe root of the resulting AVL tree in one line.
Sample Input 1:
5
88 70 61 96 120
Sample Output 1:
70
Sample Input 2:
7
88 70 61 96 120 90 65
Sample Output 2:
88
解题思路
建个avl树,没啥技巧
AC代码
#include <cstdio>#include <algorithm>using namespace std;struct node{ node *left, *right; int v, w; node(int value, node* l, node* r) : v(value), left(l), right(r), w(0) {}};node *nil = new node(0, NULL, NULL);node *head = nil;void leftrotate(node *&head){ node *t = head->right; head->right = t->left; t->left = head; head = t; head->left->w = max(head->left->right->w, head->left->left->w) + 1; head->w = max(head->right->w, head->left->w) + 1;}void rightrotate(node *&head){ node *t = head->left; head->left = t->right; t->right = head; head = t; head->right->w = max(head->right->right->w, head->right->left->w) + 1; head->w = max(head->right->w, head->left->w) + 1;}void insert(node *&head, int v){ if (head == nil){ head = new node(v, nil, nil); }else if (v > head->v){ insert(head->right, v); if (2 == head->right->w - head->left->w){ if (v > head->right->v){ leftrotate(head); }else{ rightrotate(head->right); leftrotate(head); } } }else{ insert(head->left, v); if (2 == head->left->w - head->right->w){ if (v <= head->left->v){ rightrotate(head); }else{ leftrotate(head->left); rightrotate(head); } } } head->w = max(head->left->w, head->right->w) + 1;}int main(){ int n, a; scanf("%d", &n); while (n--){ scanf("%d", &a); insert(head, a); } printf("%d\n", head->v); return 0;}
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