题目

Consider the following version of Bubble Sort:

for (int i = 0; i < n; i++) {

for (int j = 0; j < n - 1; j++) {
    // Swap adjacent elements if they are in decreasing order
    if (a[j] > a[j + 1]) {
        swap(a[j], a[j + 1]);
    }
}

}
Given an array of integers, sort the array in ascending order using the Bubble Sort algorithm above. Once sorted, print the following three lines:

Array is sorted in numSwaps swaps., where is the number of swaps that took place.
First Element: firstElement, where is the first element in the sorted array.
Last Element: lastElement, where is the last element in the sorted array.
Hint: To complete this challenge, you must add a variable that keeps a running tally of all swaps that occur during execution.

For example, given a worst-case but small array to sort: we go through the following steps:

swap a
0 [6,4,1]
1 [4,6,1]
2 [4,1,6]
3 [1,4,6]
It took swaps to sort the array. Output would be

Array is sorted in 3 swaps.
First Element: 1
Last Element: 6
Function Description

Complete the function countSwaps in the editor below. It should print the three lines required, then return.

countSwaps has the following parameter(s):

a: an array of integers .
Input Format

The first line contains an integer, , the size of the array .
The second line contains space-separated integers .

Constraints

Output Format

You must print the following three lines of output:

Array is sorted in numSwaps swaps., where is the number of swaps that took place.
First Element: firstElement, where is the first element in the sorted array.
Last Element: lastElement, where is the last element in the sorted array.
Sample Input 0

3
1 2 3
Sample Output 0

Array is sorted in 0 swaps.
First Element: 1
Last Element: 3
Explanation 0
The array is already sorted, so swaps take place and we print the necessary three lines of output shown above.

Sample Input 1

3
3 2 1
Sample Output 1

Array is sorted in 3 swaps.
First Element: 1
Last Element: 3
Explanation 1
The array is not sorted, and its initial values are: . The following swaps take place:

At this point the array is sorted and we print the necessary three lines of output shown above.

题目解析

核心就是冒泡排序以及数组取第一个值和最后一个值，同时注意slice的用法
语法
class slice(stop)
class slice(start, stop[, step])
　　参数说明
start--起始位置默认为None
stop--结束位置自定义
step--间距默认为None间距为1

Answer

#!/bin/python3

import math
import os
import random
import re
import sys

# Complete the countSwaps function below.
def countSwaps(a):
    i=0
    j=0
    n=len(a)
    sw=0
    for  i  in range(n):
        for j in range(n-1):
            if a[j] > a[j + 1]:
                a[j] ,a[j + 1]=a[j + 1],a[j]
                sw+=1
    print("Array is sorted in %d swaps." %sw)
    print("First Element: %d" %a[0])
    print("Last Element: %d" %a[-1])


if __name__ == '__main__':
    n = int(input())

    a = list(map(int, input().rstrip().split()))

    countSwaps(a)