quicksort
public class QuickSort {
public static void sort(int[] arr) {
if(arr == null || arr.length < 2) return;
quicksort(arr,0, arr.length -1);
}
public static void quicksort(int[] arr, int left, int right) {
if(left < right) {
int[] pos = partition(arr, left, right);
quicksort(arr,left,pos[0]-1);
quicksort(arr, pos[1]+1,right);
}
}
//return array[] 2 with leftboundary and rightboundary
public static int[] partition(int[] arr, int left, int right) {
if(left == right) return new int[] {left,left};
int less = left -1;
int more = right;
int target = arr[right];
while(left < more) {
if(arr[left] < target) {
swap(arr, ++less, left++);
}else if(arr[left] > target) {
swap(arr,--more,left);
}else {
left++;
}
}
swap(arr, more,right);
return new int[] {less+1, more};
}
public static void swap(int[] arr, int i, int j) {
int tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
public static void main(String[] args) {
int [] arr = {4,3,2,1};
sort(arr);
for(int i=0; i < arr.length;i++) {
System.out.println(arr[i]);
}
}
}
