快速排序的两种写法

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第一种，填坑法：

public static void quicksort(int[] array,int left,int right){
        if(left>=right) return;
        Random ra=new Random();
        int i=ra.nextInt(right-left)+left,j=right;
        int[] swap=swap(array[i],array[left]);
        array[i]=swap[0];array[left]=swap[1];
        int coreElem=array[left];
        i=left;
        while(i<j){
            while(array[j]>coreElem&&i<j){j--;}
            if(i<j) {
                array[i]=array[j];
                i++;
            }        
            
            while(array[i]<coreElem&&i<j){i++;}
            if(i<j){
                array[j]=array[i];
                j--;
            }
        }
        array[i]=coreElem;
        quicksort(array,left,i-1);
        quicksort(array,i+1,right);
}

第二种，交换法：

public static int partition(int[] array,int left,int right){
    int firstPointer=left,secondPointer=left-1;
    Random ra=new Random();
    int i=ra.nextInt(right-left)+left;
    int[] swap=swap(array[i],array[right]);
    array[i]=swap[0];array[right]=swap[1];
    while(firstPointer<right){
        if(array[firstPointer]<array[right]){
            secondPointer++;
            if(firstPointer!=secondPointer)
            swap=swap(array[firstPointer],array[secondPointer]);
            array[firstPointer]=swap[0];array[secondPointer]=swap[1];
        }
        firstPointer++;
    }
    array[++secondPointer]=array[right];
    return secondPointer; 
}

public static void quicksort(int[] array,int left,int right){
    if(left>=right) return;
    int partitionIndex=partition(array,left,right);
    if(partitionIndex>left) quicksort(array,left,partitionIndex-1);
    if(partitionIndex<right) quicksort(array,partitionIndex+1,right);
}

另附swap，java中比较简易的swap函数实现：

public static int[] swap(int a,int b){
        return new int[]{b,a};
    }