package demo67;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.TreeMap;
/**
* 取数组中的第几大数
* @author mengfeiyang
*
*/
public class GetNBig {
public static void main(String[] args) {
test25();
TreeMap<Integer,Integer> hm = new TreeMap<Integer,Integer>();
List<Integer> list = new ArrayList<Integer>();
int a[] = {1,8,6,9,0,5,7,6};
int n = 4;//取第几大的数
for(int b : a){hm.put(b, b);list.add(b);}
System.out.println("map:"+hm.values());
list.sort(new Comparator<Integer>() {
@Override
public int compare(Integer o1, Integer o2) {
return -(o1-o2);//从大到小排序
}
});
System.out.println("list:"+Arrays.toString(list.toArray()));
System.out.println(choose_nth(a,0,a.length-1,n));
fast_sort(a,0,a.length-1);
System.out.println(Arrays.toString(a));
}
//快速排序方法
public static void fast_sort(int a[], int startIndex, int endIndex)
{
int midOne = a[startIndex];//选第一个作为参考点
int i = startIndex, j = endIndex;
if(i < j)//这个判断是递归结束的依据,不加的话会导致堆栈溢出
{
while(i < j)
{
for(; i < j; j--){
if(a[j] < midOne)//小于参考点的数移到左边
{
a[i++] = a[j];
break;
}
}
for(; i < j; i++){
if(a[i] > midOne)//大于参考点的数移到右边
{
a[j--] = a[i];
break;
}
}
}
a[i] = midOne;//参考点归位
//把参考点左右的部分分别进行快排
fast_sort(a, startIndex, i - 1);
fast_sort(a, i + 1, endIndex);
}
}
//使用快速排序获取到第n大值
public static int choose_nth(int a[], int startIndex, int endIndex, int n)
{
int midOne = a[startIndex];
int i = startIndex, j = endIndex;
if(i == j) //递归出口之一
return a[i];
if(i < j)
{
while(i < j)
{
for(; i < j; j--){
if(a[j] < midOne)
{
a[i++] = a[j];
break;
}
}
for(; i < j; i++){
if(a[i] > midOne)
{
a[j--] = a[i];
break;
}
}
}
a[i] = midOne;//支点归位
int th = endIndex - i + 1;//计算下标为i的数第几大
if(th == n)//正好找到
{
return a[i];
}
else
{
if(th > n )//在支点右边找
return choose_nth(a, i + 1, endIndex, n);
else//在支点左边找第(n-th)大,因为右边th个数都比支点大
return choose_nth(a, startIndex, i - 1, n - th);
}
}
return -1;
}
public static void test21(){
int tmp = 0;
for(int i=0;i<8;i++){
for(int j=0;j<=i;j++){
System.out.print((tmp++)+"\t" );
}
System.out.println();
}
}
static int s = 8;
static int c = 0;
static int tmp = 0;
public static void test22(){
for(int j=0;j<=c;j++)System.out.print((tmp++)+"\t" );
System.out.println();
c++;
if(c<s)test22();
}
public static void test23(){
int i=0,j=0,tmp=0;
while(i<8){
j=0;
while(j<=i){
System.out.print((tmp++)+"\t" );
j++;
}
i++;
System.out.println();
}
}
public static void test24(){
int j=0,k=0;
for(int i=0;i<9;i++){
for(;j<k+i;j++){
System.out.print(j+"\t");
}
System.out.print("\n");
k=j;
}
}
public static void test25(){
int i=0,j=0,tmp=0;
do{
j=0;
do{
System.out.print((tmp++)+"\t" );
j++;
}while(j<=i);
i++;
System.out.println();
}while(i<8);
}
}
