具有严格正异或的最长子阵列

给定一个由N 个非负整数组成的数组arr[] 。任务是找到最长子数组的长度，使得这个子数组的所有元素的 XOR 严格为正。如果不存在这样的子数组，则打印-1
例子：

Input: arr[] = {1, 1, 1, 1} 
Output: 3 
Take sub-array[0:2] = {1, 1, 1} 
Xor of this sub-array is equal to 1.
Input: arr[] = {0, 1, 5, 19} 
Output: 4 
 

方法：

• 如果整个数组的 XOR 为正，则 answer 等于N 。
• 如果所有元素都是零，那么答案是-1 ，因为不可能得到严格的正 XOR。
• 否则，假设第一个正数的索引是l ，最后一个正数是r 。
• 现在索引范围[l, r]的所有元素的 XOR 必须为零，因为l之前和r之后的元素都是0 ，这不会影响 XOR 值，并且原始数组的 XOR 为0 。
• 考虑子数组A ₁ , A ₁ , …, A _r-1和A _l+1 , A _l+2 , …, A _N 。
• 第一个子数组的 XOR 值等于A[r] ，第二个子数组的 XOR 值A[l]为正。
• 返回这两个子数组中较大子数组的长度。

下面是上述方法的实现：

C++

// C++ implementation of the approach
#include 
using namespace std;
 
// Function to return the length of the
// longest sub-array having positive XOR
int StrictlyPositiveXor(int A[], int N)
{
 
    // To store the XOR
    // of all the elements
    int allxor = 0;
 
    // To check if all the
    // elements of the array are 0s
    bool checkallzero = true;
 
    for (int i = 0; i < N; i += 1) {
 
        // Take XOR of all the elements
        allxor ^= A[i];
 
        // If any positive value is found
        // the make the checkallzero false
        if (A[i] > 0)
            checkallzero = false;
    }
 
    // If complete array is the answer
    if (allxor != 0)
        return N;
 
    // If all elements are equal to zero
    if (checkallzero)
        return -1;
 
    // Initialize l and r
    int l = N, r = -1;
 
    for (int i = 0; i < N; i += 1) {
 
        // First positive value of the array
        if (A[i] > 0) {
            l = i + 1;
            break;
        }
    }
    for (int i = N - 1; i >= 0; i -= 1) {
 
        // Last positive value of the array
        if (A[i] > 0) {
            r = i + 1;
            break;
        }
    }
 
    // Maximum length among
    // these two subarrays
    return max(N - l, r - 1);
}
 
// Driver code
int main()
{
 
    int A[] = { 1, 0, 0, 1 };
 
    int N = sizeof(A) / sizeof(A[0]);
 
    cout << StrictlyPositiveXor(A, N);
 
    return 0;
}

Java

// Java implementation of the approach
import java.io.*;
 
class GFG
{
 
// Function to return the length of the
// longest sub-array having positive XOR
static int StrictlyPositiveXor(int []A, int N)
{
 
    // To store the XOR
    // of all the elements
    int allxor = 0;
 
    // To check if all the
    // elements of the array are 0s
    boolean checkallzero = true;
 
    for (int i = 0; i < N; i += 1)
    {
 
        // Take XOR of all the elements
        allxor ^= A[i];
 
        // If any positive value is found
        // the make the checkallzero false
        if (A[i] > 0)
            checkallzero = false;
    }
 
    // If complete array is the answer
    if (allxor != 0)
        return N;
 
    // If all elements are equal to zero
    if (checkallzero)
        return -1;
 
    // Initialize l and r
    int l = N, r = -1;
 
    for (int i = 0; i < N; i += 1)
    {
 
        // First positive value of the array
        if (A[i] > 0)
        {
            l = i + 1;
            break;
        }
    }
    for (int i = N - 1; i >= 0; i -= 1)
    {
 
        // Last positive value of the array
        if (A[i] > 0)
        {
            r = i + 1;
            break;
        }
    }
 
    // Maximum length among
    // these two subarrays
    return Math.max(N - l, r - 1);
}
 
// Driver code
public static void main (String[] args)
{
    int A[] = { 1, 0, 0, 1 };
 
    int N = A.length;
 
    System.out.print(StrictlyPositiveXor(A, N));
}
}
 
// This code is contributed by anuj_67..

Python3

# Python3 implementation of the approach
 
# Function to return the length of the
# longest sub-array having positive XOR
def StrictlyPositiveXor(A, N) :
 
    # To store the XOR
    # of all the elements
    allxor = 0;
 
    # To check if all the
    # elements of the array are 0s
    checkallzero = True;
 
    for i in range(N) :
 
        # Take XOR of all the elements
        allxor ^= A[i];
 
        # If any positive value is found
        # the make the checkallzero false
        if (A[i] > 0) :
            checkallzero = False;
 
    # If complete array is the answer
    if (allxor != 0) :
        return N;
 
    # If all elements are equal to zero
    if (checkallzero) :
        return -1;
 
    # Initialize l and r
    l = N; r = -1;
 
    for i in range(N) :
 
        # First positive value of the array
        if (A[i] > 0) :
            l = i + 1;
            break;
             
    for i in range(N - 1, -1, -1) :
 
        # Last positive value of the array
        if (A[i] > 0) :
            r = i + 1;
            break;
 
    # Maximum length among
    # these two subarrays
    return max(N - l, r - 1);
 
 
# Driver code
if __name__ == "__main__" :
 
    A= [ 1, 0, 0, 1 ];
    N = len(A);
    print(StrictlyPositiveXor(A, N));
 
    # This code is contributed by AnkitRai01

C#

// C# implementation of the approach
using System;
 
class GFG
{
 
// Function to return the length of the
// longest sub-array having positive XOR
static int StrictlyPositiveXor(int []A, int N)
{
 
    // To store the XOR
    // of all the elements
    int allxor = 0;
 
    // To check if all the
    // elements of the array are 0s
    bool checkallzero = true;
 
    for (int i = 0; i < N; i += 1)
    {
 
        // Take XOR of all the elements
        allxor ^= A[i];
 
        // If any positive value is found
        // the make the checkallzero false
        if (A[i] > 0)
            checkallzero = false;
    }
 
    // If complete array is the answer
    if (allxor != 0)
        return N;
 
    // If all elements are equal to zero
    if (checkallzero)
        return -1;
 
    // Initialize l and r
    int l = N, r = -1;
 
    for (int i = 0; i < N; i += 1)
    {
 
        // First positive value of the array
        if (A[i] > 0)
        {
            l = i + 1;
            break;
        }
    }
    for (int i = N - 1; i >= 0; i -= 1)
    {
 
        // Last positive value of the array
        if (A[i] > 0)
        {
            r = i + 1;
            break;
        }
    }
 
    // Maximum length among
    // these two subarrays
    return Math.Max(N - l, r - 1);
}
 
// Driver code
public static void Main ()
{
    int []A = { 1, 0, 0, 1 };
 
    int N = A.Length;
 
    Console.WriteLine(StrictlyPositiveXor(A, N));
}
}
 
// This code is contributed by anuj_67..

Javascript

 
// Javascript implementation of the approach
 
// Function to return the length of the
// longest sub-array having positive XOR
function StrictlyPositiveXor(A, N)
{
 
    // To store the XOR
    // of all the elements
    let allxor = 0;
 
    // To check if all the
    // elements of the array are 0s
    let checkallzero = true;
 
    for (let i = 0; i < N; i += 1) {
 
        // Take XOR of all the elements
        allxor ^= A[i];
 
        // If any positive value is found
        // the make the checkallzero false
        if (A[i] > 0)
            checkallzero = false;
    }
 
    // If complete array is the answer
    if (allxor != 0)
        return N;
 
    // If all elements are equal to zero
    if (checkallzero)
        return -1;
 
    // Initialize l and r
    let l = N, r = -1;
 
    for (let i = 0; i < N; i += 1) {
 
        // First positive value of the array
        if (A[i] > 0) {
            l = i + 1;
            break;
        }
    }
    for (let i = N - 1; i >= 0; i -= 1) {
 
        // Last positive value of the array
        if (A[i] > 0) {
            r = i + 1;
            break;
        }
    }
 
    // Maximum length among
    // these two subarrays
    return Math.max(N - l, r - 1);
}
 
// Driver code
 
    let A = [ 1, 0, 0, 1 ];
 
    let N = A.length;
 
    document.write(StrictlyPositiveXor(A, N));
 

输出：

3

时间复杂度： O(N)

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