LeetCode 59. Spiral Matrix IIsolution

public class Solution {
    public int[][] generateMatrix(int n) {
        if(n<0)
            return null;
        int[][] res = new int[n][n];
        
        int count = 1;
        
        int rowBegin = 0;
        int rowEnd = n-1;
        int colBegin = 0;
        int colEnd = n-1;
        
        while(rowBegin <= rowEnd && colBegin <= colEnd) {
            for(int i=colBegin;i<=colEnd;i++)
                res[rowBegin][i] = count++;
            rowBegin++;
            
            for(int i=rowBegin;i<=rowEnd;i++)
                res[i][colEnd] = count++;
            colEnd--;
            
            if(rowBegin <= rowEnd) {
                for(int i=colEnd;i>=colBegin;i--)
                    res[rowEnd][i] = count++;
                rowEnd--;
            }
            
            if(colBegin <= colEnd) {
                for(int i=rowEnd;i>=rowBegin;i--)
                    res[i][colBegin] = count++;
                colBegin++;
            }
        }
        return res;
    }
}