中国大学MOOC浙大数据结构04-树6 Complete Binary Search Tree (30分) 两种解题方法（2）

本解法与上一解法比较，采用数组名存储节点值，基本全部采用int类型，因为数值大小不超过2000，所以存储空间占得更小一点。可惜的是，对于最后一个测试点，不知为何总是答案错误，多次模拟输入也未能发现原因，望指正。

#include<queue>
#include<stdio.h>
#include<iostream>
#include<stdlib.h>
#include<algorithm>
#include<math.h>
#define null 0
#define MAXSIZE 2002
using namespace std;
struct TreeNode {
int Left;
int Right;
}T1[MAXSIZE];
int BuildTree(int a[], int i, int j)
{
int num = j - i + 1;//指示元素个数
if (num == 1)//只传进来一个元素就返回它
return a[i];
int height;//指示多少行
for (height = 0; pow(2, height) - 1 < num; height++);//num=3，height=2；num=4，height=3
int lastnum = num - pow(2, height - 1) + 1;//记录最底下一排的个数,num=4,height=3,lastnum=1;
int rightnum, leftnum;
if (lastnum > pow(2, height - 2))
{
rightnum = lastnum - pow(2, height - 2);
leftnum = lastnum - rightnum;
}
else {
rightnum = 0;
leftnum = lastnum;
}
int dif = leftnum - rightnum;
int mid = (i + j + dif) / 2;
if (mid - 1 >= i)
T1[a[mid]].Left = BuildTree(a, i, mid - 1);
else T1[a[mid]].Left = null;
if (j >= mid + 1)
T1[a[mid]].Right = BuildTree(a, mid + 1, j);
else  T1[a[mid]].Right= null;
return a[mid];
}
void LevelTraversals(int Root)
{
queue<int> Q;
int T;
Q.push(Root);
int tag = 0;
while (!Q.empty())
{
T = Q.front();
Q.pop();
if (tag == 0)
{
printf("%d", T); tag++;
}
else
printf(" %d", T);
if(T1[T].Left!=null)Q.push(T1[T].Left);
if(T1[T].Right!=null)Q.push(T1[T].Right);
}
}
int main()
{
int N;
scanf("%d", &N);
int* a = (int*)malloc((N + 1) * sizeof(int));
for (int i = 1; i <= N; i++)
scanf("%d", &a[i]);
sort(a + 1, a + N + 1);
int Root = BuildTree(a, 1, N);
LevelTraversals(Root);
return 0;
}