Question

How to generate an n x n matrix filled with elements from 1 to N^2 in spiral order in C++

Answer 1

#include <iostream>
#include <vector>

using std::vector;

vector<vector<int>> generateSpiralMatrix(int n) {
    vector<vector<int>> matrix(n, vector<int>(n));
    int top = 0, bottom = n - 1, left = 0, right = n - 1;
    int num = 1;

    while (top <= bottom && left <= right) {
        // Fill top row
        for (int i = left; i <= right; ++i) {
            matrix[top][i] = num++;
        }
        top++;

        // Fill right column
        for (int i = top; i <= bottom; ++i) {
            matrix[i][right] = num++;
        }
        right--;

        // Fill bottom row
        if (top <= bottom) {
            for (int i = right; i >= left; --i) {
                matrix[bottom][i] = num++;
            }
            bottom--;
        }

        // Fill left column
        if (left <= right) {
            for (int i = bottom; i >= top; --i) {
                matrix[i][left] = num++;
            }
            left++;
        }
    }

    return matrix;
}

int main() {
    int n = 3; // size of the matrix

    vector<vector<int>> spiralMatrix = generateSpiralMatrix(n);

    // Print the matrix
    for (const auto& row : spiralMatrix) {
        for (int val : row) {
            std::cout << val << "\t";
        }
        std::cout << std::endl;
    }
}


/*
run:

1	2	3	
8	9	4	
7	6	5

*/

 

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