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mergesort.java
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executable file
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package com.leetcode;
import java.util.Random;
/**
* Created with IntelliJ IDEA.
* User: hongtaocai
* Date: 1/22/13
* Time: 4:52 PM
* To change this template use File | Settings | File Templates.
*/
public class MergeSort {
void mergeSort(int arr[]){
int tmp[] = new int[arr.length];
mergeSort(arr,0,arr.length-1,tmp);
}
void merge(int arr[], int start, int mid, int last, int[] tmp){
int i=start;
int j=mid+1;
int k=0;
while(i<=mid && j<=last){
if(arr[i]<arr[j]){
tmp[k++]=arr[i++];
}
else{
tmp[k++]=arr[j++];
}
}
while(i<=mid){
tmp[k++]=arr[i++];
}
while(j<=last){
tmp[k++]=arr[j++];
}
for(i=0;i<k;i++){
arr[start+i]=tmp[i];
}
}
private void mergeSort(int arr[], int start, int last, int[] tmp){
if(start==last) return;
int mid = start+(last-start)/2;
mergeSort(arr,start,mid,tmp);
mergeSort(arr,mid+1,last,tmp);
merge(arr, start, mid, last, tmp);
}
public static void main(String args[]){
int a[] = new int[1000];
Random r = new Random();
boolean flag = true;
MergeSort m = new MergeSort();
loop1 :
for(int i=0;i<100;i++){
for(int j=0;j<1000;j++){
a[j] = r.nextInt();
}
m.mergeSort(a);
for(int j=1;j<1000;j++){
if(a[j]<a[j-1]){
flag = false;
break loop1;
}
}
}
System.out.println(flag);
}
}