1135 Is It A Red-Black Tree(30 分)
There is a kind of balanced binary search tree named red-black tree in the data structure. It has the following 5 properties:
For example,the tree in Figure 1 is a red-black tree,while the ones in Figure 2 and 3 are not.
For each given binary search tree,you are supposed to tell if it is a legal red-black tree. Input Specification:Each input file contains several test cases. The first line gives a positive integer K (≤30) which is the total number of cases. For each case,the first line gives a positive integer N (≤30),the total number of nodes in the binary tree. The second line gives the preorder traversal sequence of the tree. While all the keys in a tree are positive integers,we use negative signs to represent red nodes. All the numbers in a line are separated by a space. The sample input cases correspond to the trees shown in Figure 1,2 and 3. Output Specification:For each test case,print in a line "Yes" if the given tree is a red-black tree,or "No" if not. Sample Input:3 9 7 -2 1 5 -4 -11 8 14 -15 9 11 -2 1 -7 5 -4 8 14 -15 8 10 -7 5 -6 8 15 -11 17 Sample Output:
#include <iostream> #include <cstdio> #include <cstring> #include <vector> #include <algorithm> using namespace std; struct tree { int data; tree *left,*right; }; int pre[31],in[31]; int k,n,flag; tree *build(int pre_l,int pre_r,int in_l,int in_r) { tree *t = new tree(); t -> left = t -> right = NULL; for(int i = in_l;i <= in_r;i ++) { if(in[i] == abs(pre[pre_l])) { if(i != in_l)t -> left = build(pre_l + 1,pre_l + i - in_l,in_l,i - 1); if(i != in_r)t -> right = build(pre_l + i - in_l + 1,pre_r,i + 1,in_r); break; } } t -> data = pre[pre_l]; return t; } int check(tree *t) { if(t == NULL)return 1; if(t -> data < 0 && (t -> left && t -> left -> data < 0 || t -> right && t -> right -> data < 0)) { flag = 0; return 0; } int d = check(t -> left),e = check(t -> right); if(d != e)flag = 0; return d + (t -> data > 0);///如果颜色为黑色,返回值加1 } void drop(tree *t) { if(t == NULL)return; drop(t -> left); drop(t -> right); delete t; } int main() { scanf("%d",&k); while(k --) { scanf("%d",&n); for(int i = 0;i < n;i ++) { scanf("%d",&pre[i]); in[i] = abs(pre[i]);///取绝对值 } flag = 1; sort(in,in + n); tree *head = build(0,n - 1,0,n - 1);///建树 if(head -> data < 0)flag = 0;///根结点不是黑色 else check(head);///检查是否满足 drop(head);///释放空间 puts(flag ? "Yes" : "No"); } } (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |