59. Spiral Matrix II

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Problem

Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

Example:

Input: 3
Output:
[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

Code

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        if(n == 0){
            return matrix;
        }

        int rowBegin = 0;
        int rowEnd = n - 1;
        int colBegin = 0;
        int colEnd = n - 1;
        int num = 1;

        while(rowBegin <= rowEnd && colBegin <= colEnd){
            for(int i = colBegin; i <= colEnd; i++){
                matrix[rowBegin][i] = num++;
            }
            rowBegin++;

            for(int i = rowBegin; i <= rowEnd; i++ ){
                matrix[i][colEnd] = num++;
            }
            colEnd--;

            for(int i = colEnd; i >= colBegin; i--){
                matrix[rowEnd][i] = num++;
            }
            rowEnd--;

            for(int i = rowEnd; i >= rowBegin; i--){
                matrix[i][colBegin] = num++;
            }
            colBegin++;
        }
        return matrix;
    }
}