# 5. 快速排序

nlogn

一句话总结：

> 选定一个 目标值
>
> 左边寻找比目标值大的，右边寻找比目标值小的，替换
>
> 最后左右轴相交，把左轴值和目标值对换，返回左轴索引
>
> 递归对每个二分区间执行同样操作

python

```python
def part_sort(array, left, right):
    tag = right
    key = array[tag]
    while left < right:
        # 左边位置，移到左边第一个比key大的位置
        while left < right and array[left] <= key:
            left += 1
        # 右边位置，移到右边第一个
        while left < right and array[right] >= key:
            right -= 1
        array[left], array[right] = array[right], array[left]
    # 因为先左边执行while，所以此时的arrar[left]一定是>=key的，因此arrar[left]可以和arrar[tag]交换，以满足左边对的不大于右边
    array[left], array[tag] = array[tag], array[left]
    return left


def quicksort(array, left, right):
    if left >= right: return
    stack = []
    stack.append([left, right])
    while len(stack) != 0:
        out = stack.pop()
        center = part_sort(array, out[0], out[1])
        if center - 1 > out[0]:
            stack.append([out[0], center - 1])
        if center + 1 < out[1]:
            stack.append([center + 1, out[1]])


if __name__ == '__main__':
    data = [16, 25, 39, 27, 12, 8, 45, 63]
    quicksort(data, 0, len(data) - 1)
    print(data)
```

java

```java
public abstract class Sort<T extends Comparable<T>> {
    public abstract void sort(T[] nums);

    public boolean less(T v,T w){
        return v.compareTo(w)<0;
    }

    public void swap(T[] a,int i,int j){
        T t=a[i];
        a[i]=a[j];
        a[j]=t;
    }
}

public class QuickSort<T extends Comparable<T>> extends Sort<T> {
    @Override
    public void sort(T[] nums) {
        shuffle(nums);
        sort(nums,0,nums.length-1);
    }

    public void sort(T[] nums,int l,int h){
        if(l>=h) return;
        int j=partition(nums,l,h);
        sort(nums,l,j-1);
        sort(nums,j+1,h);
    }

    public int partition(T[] nums,int l,int h){
        int i=l,j=h+1;
        T v=nums[l];
        while(true){
            while(j!=l&&less(v,nums[--j]));
            while(i!=h&&less(nums[++i],v));
            if(i>=j) break;
            swap(nums,i,j);
        }
        swap(nums,l,j);
        return j;
    }

    public void shuffle(T[] nums){
        List<Comparable> list=Arrays.asList(nums);
        Collections.shuffle(list);
        list.toArray(nums);
    }

    public static void main(String[] args){
        Integer[] arr={
                5,1,8,7,10,6,9,5,20,3,0
        };
        Sort<Integer> sort=new QuickSort<>();
        sort.sort(arr);
        ArrayUtils.printArray(arr);
    }
}
```


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