import java.util.Arrays;

public class MergeSort {

public static int[] mergeSort(int[] arry,int start, int end){

if(start > end){

if(start > arry.length-1){

return null;

}

int[] tmp = {arry[start]};

return tmp;

}

int mid = (start+end)/2;

int[] left = mergeSort(arry,start,mid-1);

int [] right = mergeSort(arry,mid+1,end);

return merge(left,right);

}

public static int[] merge(int[] a, int[] b){

if(a==null||b==null) return a==null?b:a;

int[] tmp = new int[a.length+b.length];

int alen = a.length-1;

int blen = b.length-1;

int cur = 0;

int acur = 0;

int bcur = 0;

if(a[0]>b[blen]){

for(int i=0;i<b.length;i++){

tmp[i] = b[i];

}

int index = 0;

for(int j=b.length;j<tmp.length;j++){

tmp[j] = a[index];

index++;

}

}else if(b[0]>a[alen]){

for(int i=0;i<a.length;i++){

tmp[i] = a[i];

}

int index=0;

for(int j=a.length;j<tmp.length;j++){

tmp[j] = b[index];

index++;

}

}else{

while( cur < tmp.length){

if(acur>alen){

tmp[cur] = b[bcur];

cur++;

bcur++;

continue;

}

if(bcur>blen){

tmp[cur] = a[acur];

cur++;

acur++;

continue;

}

if(a[acur]<=b[bcur]){

tmp[cur] = a[acur];

acur++;

cur++;

}else{

tmp[cur] = b[bcur];

bcur++;

cur++;

}

}

}

return tmp;

}

public static void main(String args[]){

int[] a = {7,5,3,2,1,6,9};

System.out.println(Arrays.toString(mergeSort(a,0,a.length-1)));

}

}