什么时候应该使用while循环和if语句？

Question

I was trying out a question where you have to swap the adjacent elements in an array based on the number of swaps given. For example:

Suppose, no of swaps = 2, and the array is [5,3,1]. Then the sorted array after two successful swaps will be [3,5,1] --> 1st swap, [3,1,5] --> 2nd swap. So sorted array is [1,3,5].

This is my code on achieving the above result:

T = int(input())                 # This is the number of testcases
l = 0
for i in range(T):
    N, K = input().split()       # N is the size of array, K is the number of swaps needed to be done
    N, K = int(N), int(K)
    A = input().split(" ", N)    # A is the array of elements
    for j in range(len(A)):
        A[j] = int(A[j])

    while K != 0:
        for k in range(l+1, N):
            if A[l] > A[k]:
                A[l], A[k] = A[k], A[l]
                K -= 1
                l = 0
            else:
                l += 1
            break
    
    for j in A:
        print(j, end=" ")
    l = 0
    print()

At first, when I tried out if K!=0 only 1 swap was done. Only after using while K!=0 , the code worked perfectly. So,my question is why didn't it work for the if statement? When is it appropriate to use if and while ?

Answer 1

  T=int(input()) 
  for _ in range(T):
                        [N,K]=list(map(int, input().rstrip().split()))
                        arr = list(map(int, input().rstrip().split()))
                        
                        for i in range(K):
                                            arr[i],arr[i+1]=arr[i+1],arr[i]
                                           
                        print(*arr)

Is this what are you trying to get? Swap as you iterate through the list and stop when you have reached the swapping limit.

Answer 2

if will only check the value of k once, while will continue(like a loop) what in the scope till your condition is false you can use while if you are waiting for a specific action to stop/break, and if when need to check something at a time. I hope that was clear. in your case for will works well.