自底向上的归并排序-转自算法C语言实现

package cn.ccnu.lzc;

import java.util.Random;

public class DownTopTwoWayMergeSort {

/**
* @param args
*  自底向上的归并排序：归并排序主要是完成将若干个有序子序列合并成一个
*  完整的有序子序列；自底向上的排序是归并排序的一种实现方式，将一个无
*  序的N长数组切个成N个有序子序列，然后再两两合并，然后再将合并后的N/2
*  （或者N/2 + 1）个子序列继续进行两两合并，以此类推得到一个完整的有序数组。
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int maxSize=16;
TArray arr=new TArray(maxSize);
for(int i=0;i<maxSize;i++){
int n=new Random().nextInt(100);
arr.insert(n);
}
arr.display();
arr.MergeSort();
arr.display();
}

}
class TArray{
private int[] theArray;
private int nElems;
public TArray(int max){
theArray=new int[max];
nElems=0;
}
public void insert(int value){
theArray[nElems++]=value;
}
public void display(){
for(int i:theArray){
System.out.print(i+" ");
}
System.out.println();
}
public void MergeSort(){
int[] workspace=new int[nElems];
recMergeSort(workspace,0,nElems-1);
}
private void recMergeSort(int[] workspace, int lowerBound, int upperBound) {
// TODO Auto-generated method stub
int i,step;
for(step=1;step<upperBound;step=2*step){
for(i=0;i<=upperBound-step;i+=2*step){
Merge(workspace,i,i+step,min(i+2*step-1,upperBound));
}
}

}
private void Merge(int[] workspace, int lowPtr, int highPtr, int upperBound) {
// TODO Auto-generated method stub
int lowBound=lowPtr;
int mid=highPtr-1;
int j=0;
int n=upperBound-lowBound+1;
while(lowPtr<=mid&&highPtr<=upperBound){
if(theArray[lowPtr]<=theArray[highPtr]){
workspace[j++]=theArray[lowPtr++];
}else{
workspace[j++]=theArray[highPtr++];
}
}
while(lowPtr<=mid){
workspace[j++]=theArray[lowPtr++];
}
while(highPtr<=upperBound){
workspace[j++]=theArray[highPtr++];
}
for(j=0;j<n;j++){
theArray[lowBound++]=workspace[j];
}
}
private int min(int i, int upperBound) {
// TODO Auto-generated method stub
return (i<upperBound)?i:upperBound;
}

}