05-快速排序（python、oc）

• 最优时间复杂度：O(nlogn)
• 最坏时间复杂度：O(n2)
• 稳定性：不稳定

python

# coding:utf-8

def quick_sort(alist, first, last):
    """快速排序"""
    if first > last:
        return

    mid_value = alist[first]
    low = first
    high = last

    while high > low:
        while high > low and alist[high] >= mid_value:
            high -= 1
        alist[low] = alist[high]

        while high > low and alist[low] < mid_value:
            low += 1
        alist[high] = alist[low]
    alist[low] = mid_value

    quick_sort(alist, first, low - 1)
    quick_sort(alist, low + 1, last)

if __name__ == "__main__":
    li = [54, 26, 93, 17, 77, 31, 44, 55, 20]
    print(li)
    quick_sort(li, 0, len(li)-1)
    print(li)

objective-c

/**
 快速排序
 */
- (void)quick_sort:(NSMutableArray *)arr first:(NSInteger)first last:(NSInteger)last
{
    if (first > last) {
        return;
    }
    NSInteger low = first;
    NSInteger high = last;
    NSNumber *mid_value = arr[first];
    
    while (high > low) {
        while (high > low && arr[high] >= mid_value) {
            high--;
        }
        arr[low] = arr[high];
        
        while (high > low && arr[low] < mid_value) {
            low++;
        }
        arr[high] = arr[low];
    }
    arr[high] = mid_value;
    
    [self quick_sort:arr first:first last:high - 1];
    
    [self quick_sort:arr first:high + 1 last:last];
}

示例图