快排的3种方式

//（前两种时间复杂度为o(n^2) , 最后一种为o(n*logn）

public static void swap(int[] arr , int i , int j){
    arr[i] =arr[i] ^arr[j];
    arr[j] =arr[i] ^arr[j];
    arr[i] =arr[i] ^arr[j];
}
//使数组中以arr[R]划分，返回循环后arr[R]的所在地
public static int partition(int[] arr , int L ,int R ){
    if(L >R ){
        return -1;
    }
    if(L == R ){
        return L;
    }
    int lessEqual = L-1;
    int index = L;
    while (index <R ){
        if(arr[index] <=arr[R]){
            swap(arr ,index++ , ++lessEqual);
        }
    }
    swap(arr , ++lessEqual , R);
    return lessEqual;
}

//把一个数组以arr[R]划分，返回的是值为arr[R]的区间
public static int[] netherlandsFlag(int[] arr , int L , int R){
    if(L>R){
        return new int[] { -1 ,-1};
    }
    if(L ==R){
        return new int[] {L ,R};
    }
    int less = L-1;
    int more =R;
    int index = L;
    while (index <more){
        if(arr[index] ==arr[R]){
            index++;
        }else if(arr[index] <arr[R]){
            swap(arr ,index++ , ++less);
        }else{
            swap(arr ,index , --more);
        }
    }
    swap(arr ,more ,R );
    return new int[] {less+1 , more};
}
//递归1
public static void process1(int[] arr ,int L ,int R ){
    if(L >=R){
        return;
    }
    int M =partition(arr ,L ,R);
    process1(arr , L , M-1);
    process1(arr , M+1 ,R);
}
//快排1
public static void quickSort1(int[] arr){
    if(arr ==null || arr.length <2){
        return;
    }
    process1(arr ,0 , arr.length-1);
}

//递归2
public static void process2(int[] arr ,int L ,int R){
    if(L >=R){
        return;
    }
    int[] equalArea =netherlandsFlag(arr ,L ,R);
    process2(arr ,L ,equalArea[0] -1);
    process2(arr , equalArea[1] , R);
}
//快排2
public static void quickSort2(int[] arr){
    if(arr ==null || arr.length <2){
        return;
    }
    process2(arr ,0 , arr.length-1);
}

//递归3
public static void process3(int[] arr , int L ,int R){
    if(L > R ){
        return;
    }
    swap(arr ,L + (int) (Math.random() * (R - L+1)), R);
    int[] equalArea = netherlandsFlag(arr , L ,R);
    process3(arr , L , equalArea[0] -1);
    process3(arr , equalArea[1] +1, R );
}
//快排3
public static void quickSort3(int[] arr){
    if(arr == null ||arr.length <2){
        return;
    }
    process3(arr , 0  , arr.length-1);
}