數據結構與算法--6.二分查找

一. 二分查找

二. 代碼實現一：使用遞歸

def binary_search(alist, item):
    """二分查找：使用遞歸"""
    n = len(alist)
    if n > 0:
        mid = n // 2
        if alist[mid] == item:
            return True
        elif item < alist[mid]:
            return binary_search(alist[:mid],item)
        else:
            return binary_search(alist[mid+1:],item)
    return False

if __name__ == '__main__':
    li = [17,20,26,31,44,54,55,77,93]
    print(binary_search(li,55))
    print(binary_search(li,100))

三. 代碼實現二：非遞歸

def binary_search_2(alist,item):
    """二分查找：非遞歸"""
    n = len(alist)
    first = 0
    last = n-1
    while first <= last:
        mid = (first + last)//2
        if alist[mid] == item:
            return True
        elif item < alist[mid]:
            last = mid-1
        else:
            first = mid + 1
    return False


if __name__ == '__main__':
    li = [17,20,26,31,44,54,55,77,93]
    print(binary_search_2(li,55))
    print(binary_search_2(li,100))