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# Sort 1 to N by swapping adjacent elements

• Difficulty Level : Easy
• Last Updated : 09 Dec, 2022

Given an array, A of size N consisting of elements 1 to N. A boolean array B consisting of N-1 elements indicates that if B[i] is 1, then A[i] can be swapped with A[i+1].
Find out if A can be sorted by swapping elements.

Examples:

```Input : A[] = {1, 2, 5, 3, 4, 6}
B[] = {0, 1, 1, 1, 0}
Output : A can be sorted
We can swap A[2] with A[3] and then A[3] with A[4].

Input : A[] = {2, 3, 1, 4, 5, 6}
B[] = {0, 1, 1, 1, 1}
Output : A can not be sorted
We can not sort A by swapping elements as 1 can never be swapped with A[0]=2.```

Method 1: Here we can swap only A[i] with A[i+1]. So to find whether array can be sorted or not. Using boolean array B we can sort array for a continuous sequence of 1 for B. At last, we can check, if A is sorted or not.

Below is the implementation of the above approach:

## C++

 `// CPP program to test whether array` `// can be sorted by swapping adjacent` `// elements using boolean array` `#include ` `using` `namespace` `std;`   `// Return true if array can be` `// sorted otherwise false` `bool` `sortedAfterSwap(``int` `A[], ``bool` `B[], ``int` `n)` `{` `    ``int` `i, j;`   `    ``// Check bool array B and sorts` `    ``// elements for continuous sequence of 1` `    ``for` `(i = 0; i < n - 1; i++) {` `        ``if` `(B[i]) {` `            ``j = i;` `            ``while` `(B[j])` `                ``j++;`   `            ``// Sort array A from i to j` `            ``sort(A + i, A + 1 + j);` `            ``i = j;` `        ``}` `    ``}`   `    ``// Check if array is sorted or not` `    ``for` `(i = 0; i < n; i++) {` `        ``if` `(A[i] != i + 1)` `            ``return` `false``;` `    ``}`   `    ``return` `true``;` `}`   `// Driver program to test sortedAfterSwap()` `int` `main()` `{` `    ``int` `A[] = { 1, 2, 5, 3, 4, 6 };` `    ``bool` `B[] = { 0, 1, 1, 1, 0 };` `    ``int` `n = ``sizeof``(A) / ``sizeof``(A[0]);`   `    ``if` `(sortedAfterSwap(A, B, n))` `        ``cout << ``"A can be sorted\n"``;` `    ``else` `        ``cout << ``"A can not be sorted\n"``;`   `    ``return` `0;` `}`

## Java

 `import` `java.util.Arrays;`   `// Java program to test whether an array` `// can be sorted by swapping adjacent` `// elements using boolean array`   `class` `GFG {`   `    ``// Return true if array can be` `    ``// sorted otherwise false` `    ``static` `boolean` `sortedAfterSwap(``int` `A[],` `                                   ``boolean` `B[], ``int` `n)` `    ``{` `        ``int` `i, j;`   `        ``// Check bool array B and sorts` `        ``// elements for continuous sequence of 1` `        ``for` `(i = ``0``; i < n - ``1``; i++) {` `            ``if` `(B[i]) {` `                ``j = i;` `                ``while` `(B[j]) {` `                    ``j++;` `                ``}` `                ``// Sort array A from i to j` `                ``Arrays.sort(A, i, ``1` `+ j);` `                ``i = j;` `            ``}` `        ``}`   `        ``// Check if array is sorted or not` `        ``for` `(i = ``0``; i < n; i++) {` `            ``if` `(A[i] != i + ``1``) {` `                ``return` `false``;` `            ``}` `        ``}`   `        ``return` `true``;` `    ``}`   `    ``// Driver program to test sortedAfterSwap()` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int` `A[] = { ``1``, ``2``, ``5``, ``3``, ``4``, ``6` `};` `        ``boolean` `B[] = { ``false``, ``true``, ``true``, ``true``, ``false` `};` `        ``int` `n = A.length;`   `        ``if` `(sortedAfterSwap(A, B, n)) {` `            ``System.out.println(``"A can be sorted"``);` `        ``}` `        ``else` `{` `            ``System.out.println(``"A can not be sorted"``);` `        ``}` `    ``}` `}`

## Python3

 `# Python 3 program to test whether an array` `# can be sorted by swapping adjacent` `# elements using a boolean array`     `# Return true if array can be` `# sorted otherwise false` `def` `sortedAfterSwap(A, B, n) :`   `    ``# Check bool array B and sorts` `    ``# elements for continuous sequence of 1` `    ``for` `i ``in` `range``(``0``, n ``-` `1``) :` `        ``if` `(B[i]``=``=` `1``) :` `            ``j ``=` `i` `            ``while` `(B[j]``=``=` `1``) :` `                ``j ``=` `j ``+` `1` ` `  `            ``# Sort array A from i to j` `            ``A ``=` `A[``0``:i] ``+` `sorted``(A[i:j ``+` `1``]) ``+` `A[j ``+` `1``:]` `            ``i ``=` `j` `        `  `        `  `    ``# Check if array is sorted or not` `    ``for` `i ``in` `range``(``0``, n) :` `        ``if` `(A[i] !``=` `i ``+` `1``) :` `            ``return` `False` `    `  ` `  `    ``return` `True`   ` `  `# Driver program to test sortedAfterSwap()` `A ``=` `[ ``1``, ``2``, ``5``, ``3``, ``4``, ``6` `]` `B ``=` `[ ``0``, ``1``, ``1``, ``1``, ``0` `]` `n ``=` `len``(A)`   `if` `(sortedAfterSwap(A, B, n)) :` `    ``print``(``"A can be sorted"``)` `else` `:` `    ``print``(``"A can not be sorted"``)` `    `    `# This code is contributed` `# by Nikita Tiwari.`

## C#

 `// C# program to test whether array` `// can be sorted by swapping adjacent` `// elements using boolean array` `using` `System;` `class` `GFG {`   `    ``// Return true if array can be` `    ``// sorted otherwise false` `    ``static` `bool` `sortedAfterSwap(``int``[] A,` `                                ``bool``[] B,` `                                ``int` `n)` `    ``{` `        ``int` `i, j;`   `        ``// Check bool array B and sorts` `        ``// elements for continuous sequence of 1` `        ``for` `(i = 0; i < n - 1; i++) {` `            ``if` `(B[i]) {` `                ``j = i;` `                ``while` `(B[j]) {` `                    ``j++;` `                ``}` `                ``// Sort array A from i to j` `                ``Array.Sort(A, i, 1 + j);` `                ``i = j;` `            ``}` `        ``}`   `        ``// Check if array is sorted or not` `        ``for` `(i = 0; i < n; i++) {` `            ``if` `(A[i] != i + 1) {` `                ``return` `false``;` `            ``}` `        ``}`   `        ``return` `true``;` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `Main()` `    ``{` `        ``int``[] A = { 1, 2, 5, 3, 4, 6 };` `        ``bool``[] B = { ``false``, ``true``, ``true``, ``true``, ``false` `};` `        ``int` `n = A.Length;`   `        ``if` `(sortedAfterSwap(A, B, n)) {` `            ``Console.WriteLine(``"A can be sorted"``);` `        ``}`   `        ``else` `{` `            ``Console.WriteLine(``"A can not be sorted"``);` `        ``}` `    ``}` `}`   `// This code is contributed by Sam007`

## PHP

 ``

## Javascript

 ``

Output:

`A can be sorted`

Time Complexity: O(n*n*logn), where n time is used for iterating and n*logn for sorting inside the array
Auxiliary Space: O(1), as no extra space is required

Method 2:

Here we discuss a very intuitive approach which too gives the answer in O(n) time for all cases. The idea here is that whenever the binary array has 1, we check if that index in array A has i+1 or not. If it does not contain i+1, we simply swap a[i] with a[i+1].

The reason for this is that the array should have i+1 stored at index i. And if at all the array is sortable, then the only operation allowed is swapping. Hence, if the required condition is not satisfied, we simply swap. If the array is sortable, swapping will take us one step closer to the correct answer. And as expected, if the array is not sortable, then swapping would lead to just another unsorted version of the same array.

Below is the implementation of the above approach:

## C++

 `// CPP program to test whether array` `// can be sorted by swapping adjacent` `// elements using boolean array` `#include ` `using` `namespace` `std;`   `// Return true if array can be` `// sorted otherwise false` `bool` `sortedAfterSwap(``int` `A[], ``bool` `B[], ``int` `n)` `{` `    ``for` `(``int` `i = 0; i < n - 1; i++) {` `        ``if` `(B[i]) {` `            ``if` `(A[i] != i + 1)` `                ``swap(A[i], A[i + 1]);` `        ``}` `    ``}`   `    ``// Check if array is sorted or not` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``if` `(A[i] != i + 1)` `            ``return` `false``;` `    ``}`   `    ``return` `true``;` `}`   `// Driver program to test sortedAfterSwap()` `int` `main()` `{` `    ``int` `A[] = { 1, 2, 5, 3, 4, 6 };` `    ``bool` `B[] = { 0, 1, 1, 1, 0 };` `    ``int` `n = ``sizeof``(A) / ``sizeof``(A[0]);`   `    ``if` `(sortedAfterSwap(A, B, n))` `        ``cout << ``"A can be sorted\n"``;` `    ``else` `        ``cout << ``"A can not be sorted\n"``;`   `    ``return` `0;` `}`

## Java

 `// Java program to test whether an array` `// can be sorted by swapping adjacent` `// elements using boolean array` `import` `java.io.*;`   `class` `GFG` `{` `    ``// Return true if array can be` `    ``// sorted otherwise false` `    ``static` `int` `sortedAfterSwap(``int``[] A, ` `                            ``int``[] B, ``int` `n)` `    ``{` `        ``int` `t = ``0``;` `        ``for` `(``int` `i = ``0``; i < n - ``1``; i++) ` `        ``{` `            ``if` `(B[i] != ``0``) ` `            ``{` `                ``if` `(A[i] != i + ``1``)` `                    ``t = A[i];` `                    ``A[i] = A[i + ``1``];` `                    ``A[i + ``1``] = t;` `            ``}` `        ``}` `    `  `        ``// Check if array is sorted or not` `        ``for` `(``int` `i = ``0``; i < n; i++)` `        ``{` `            ``if` `(A[i] != i + ``1``)` `                ``return` `0``;` `        ``}` `    `  `        ``return` `1``;` `    ``}` `    `  `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int``[] A = { ``1``, ``2``, ``5``, ``3``, ``4``, ``6` `};` `        ``int``[] B = { ``0``, ``1``, ``1``, ``1``, ``0` `};` `        ``int` `n = A.length;` `    `  `        ``if` `(sortedAfterSwap(A, B, n) == ``0``)` `            ``System.out.println(``"A can be sorted"``);` `        ``else` `            ``System.out.println(``"A can not be sorted"``);` `    ``}` `}`   `// This code is contributed ` `// by Mukul Singh.`

## Python3

 `# Python3 program to test whether array ` `# can be sorted by swapping adjacent ` `# elements using boolean array `   `# Return true if array can be ` `# sorted otherwise false ` `def` `sortedAfterSwap(A,B,n):` `    ``for` `i ``in` `range``(``0``,n``-``1``):` `        ``if` `B[i]:` `            ``if` `A[i]!``=``i``+``1``:` `                ``A[i], A[i``+``1``] ``=` `A[i``+``1``], A[i]`   `    ``# Check if array is sorted or not` `    ``for` `i ``in` `range``(n):` `        ``if` `A[i]!``=``i``+``1``:` `            ``return` `False` `    ``return` `True`   `# Driver program` `if` `__name__``=``=``'__main__'``:` `    ``A ``=` `[``1``, ``2``, ``5``, ``3``, ``4``, ``6``]` `    ``B ``=` `[``0``, ``1``, ``1``, ``1``, ``0``]` `    ``n ``=``len``(A)` `    ``if` `(sortedAfterSwap(A, B, n)) :` `        ``print``(``"A can be sorted"``) ` `    ``else` `:` `        ``print``(``"A can not be sorted"``) `   `# This code is contributed by ` `# Shrikant13`

## C#

 `// C# program to test whether array` `// can be sorted by swapping adjacent` `// elements using boolean array` `using` `System;`   `class` `GFG` `{` `    ``// Return true if array can be` `    ``// sorted otherwise false` `    ``static` `int` `sortedAfterSwap(``int``[] A, ` `                               ``int``[] B, ``int` `n)` `    ``{` `        ``int` `t = 0;` `        ``for` `(``int` `i = 0; i < n - 1; i++) ` `        ``{` `            ``if` `(B[i] != 0) ` `            ``{` `                ``if` `(A[i] != i + 1)` `                    ``t = A[i];` `                    ``A[i] = A[i + 1];` `                    ``A[i + 1] = t;` `            ``}` `        ``}` `    `  `        ``// Check if array is sorted or not` `        ``for` `(``int` `i = 0; i < n; i++)` `        ``{` `            ``if` `(A[i] != i + 1)` `                ``return` `0;` `        ``}` `    `  `        ``return` `1;` `    ``}` `    `  `    ``// Driver Code` `    ``public` `static` `void` `Main()` `    ``{` `        ``int``[] A = { 1, 2, 5, 3, 4, 6 };` `        ``int``[] B = { 0, 1, 1, 1, 0 };` `        ``int` `n = A.Length;` `    `  `        ``if` `(sortedAfterSwap(A, B, n) == 0)` `            ``Console.WriteLine(``"A can be sorted"``);` `        ``else` `            ``Console.WriteLine(``"A can not be sorted"``);` `    ``}` `}`   `// This code is contributed ` `// by Akanksha Rai`

## PHP

 ``

## Javascript

 ``

Output

`A can be sorted`

Time Complexity: O(n)
Auxiliary Space: O(1), since no extra space has been taken.

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