Python中给定一个数组a = [2,3,9,1,0]，找出其中最大的一个数，并打印出来 求解?

Python有内置的max函数可以取最大值：

max([2,3,9,1,0])

也可以使用sorted先排序，再索引取出最大值：

sorted([2,3,9,1,0])[-1]

如果不用内置函数，自己排序算法来找出最大值，也有很多选择。

比如冒泡排序、循环排序、交换排序、插入排序、选择排序等等。

1、冒泡排序

是一种简单的排序算法。它重复地走访过要排序的数列，一次比较两个元素，如果它们的顺序错误就把它们交换过来。

def bubble_sort(arr, simulation=False):
    def swap(i, j):
        arr[i], arr[j] = arr[j], arr[i]

    n = len(arr)
    swapped = True
    
    iteration = 0
    if simulation:
        print("iteration",iteration,":",*arr)
    x = -1
    while swapped:
        swapped = False
        x = x + 1
        for i in range(1, n-x):
            if arr[i - 1] > arr[i]:
                swap(i - 1, i)
                swapped = True
                if simulation:
                    iteration = iteration + 1
                    print("iteration",iteration,":",*arr)
                    
    return arr
print(bubble_sort([2,4,5,1]))

2.循环排序

def cycle_sort(arr):
    len_arr = len(arr)
    for cur in range(len_arr - 1):
        item = arr[cur]
        index = cur
        for i in range(cur + 1, len_arr):
            if arr[i] < item:
                index += 1
        if index == cur:
            continue
        while item == arr[index]:
            index += 1
        arr[index], item = item, arr[index]
        while index != cur:
            index = cur
            for i in range(cur + 1, len_arr):
                if arr[i] < item:
                    index += 1
            while item == arr[index]:
                index += 1
            arr[index], item = item, arr[index]
    return arr
print(cycle_sort([2,4,5,1]))

3、交换排序

def exchange_sort(arr):
    arr_len = len(arr)
    for i in range(arr_len-1):
        for j in range(i+1, arr_len):
            if(arr[i] > arr[j]):
                arr[i], arr[j] = arr[j], arr[i]
    return arr
print(exchange_sort([2,4,5,1]))

4、插入排序

def insertion_sort(arr, simulation=False):
    iteration = 0
    if simulation:
        print("iteration",iteration,":",*arr)
    for i in range(len(arr)):
        cursor = arr[i]
        pos = i
        while pos > 0 and arr[pos - 1] > cursor:
            # Swap the number down the list
            arr[pos] = arr[pos - 1]
            pos = pos - 1
        arr[pos] = cursor
        if simulation:
                iteration = iteration + 1
                print("iteration",iteration,":",*arr)

    return arr
print(insertion_sort([2,4,5,1]))

5、选择排序

def selection_sort(arr, simulation=False):
    iteration = 0
    if simulation:
        print("iteration",iteration,":",*arr)   
    for i in range(len(arr)):
        minimum = i
        for j in range(i + 1, len(arr)):
            # "Select" the correct value
            if arr[j] < arr[minimum]:
                minimum = j
        arr[minimum], arr[i] = arr[i], arr[minimum]
        if simulation:
                iteration = iteration + 1
                print("iteration",iteration,":",*arr)
    return arr

print(selection_sort([2,4,5,1]))

通过排序算法得到顺序列表后，通过索引就可以得到最大值，so easy！