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Understanding the 'Next Permutation' Algorithm in Java

Understanding the 'Next Permutation' Algorithm in Java

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Jordan
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2 min read

Hey Coders! 👋 Today, let's dive into the Java code for the 'Next Permutation' algorithm – a handy tool for generating the next lexicographically greater permutation of an array.

public class Solution {
    public int[] nextPermutation(int[] A) {
        // Code Magic Unleashed
    }
}

Checking the Current Sequence:

We kick off by scanning the array to see if it's already in ascending order, indicating room for a greater permutation.

int count = 0;
for (int i = 1; i < A.length; i++) {
    if (A[i] > A[i - 1]) {
        count++;
        break;
    }
}

Rearranging for a Fresh Start:

If the array is already at its peak permutation, we perform a straightforward reversal to reset the order.

if (count == 0) {
    int i = 0;
    int j = A.length - 1;
    while (i < j) {
        int temp = A[i];
        A[i] = A[j];
        A[j] = temp;
        i++;
        j--;
    }
    return A;  // Done and Dusted!
}

Identifying the Pivot:

Now, we identify a pivot point where a change in the permutation is needed.

int a = 0;
for (int i = A.length - 1; i > 0; i--) {
    if (A[i - 1] < A[i]) {
        a = i;
        break;
    }
}

Swapping to Form a New Sequence:

In the heart of the algorithm, we execute a swap at the pivot point, ensuring the formation of a new lexicographically greater permutation.

for (int i = A.length - 1; i > a - 1; i--) {
    if (A[i] > A[a - 1]) {
        int temp = A[a - 1];
        A[a - 1] = A[i];
        A[i] = temp;
        break;
    }
}

Final Exchange for Completion:

The last step involves a final exchange beyond the pivot point, completing the generation of the next permutation.

int b = A.length - 1;
while (a < b) {
    int temp1 = A[a];
    A[a] = A[b];
    A[b] = temp1;
    a++;
    b--;
}
return A;  // The End

In Summary:

This Java code elegantly navigates the complexities of generating the next lexicographically greater permutation. Understanding these steps opens the door to manipulating arrays efficiently in various applications.

#NextPermutation #JavaAlgorithm

Happy coding! 🚀👩‍💻

Jordan ^_~

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