Spiral Matrix

public class Solution {
    public ArrayList<Integer> spiralOrder(int[][] matrix) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ArrayList<Integer> result = new ArrayList<Integer>();
        if(matrix == null||matrix.length == 0)
            return result;
        int m = matrix.length;
        int n = matrix[0].length;
        spiralRecur(matrix, 0, result, m, n);
        return result;
    }
    
    private void spiralRecur(int[][] matrix, int layer, ArrayList<Integer> result, int m, int n){
        int mlen = m - 2 * layer;
        int nlen = n - 2 * layer;
        
        if(mlen <= 0 || nlen <= 0)
            return;
        if(mlen == 1 && nlen == 1)
            result.add(matrix[layer][layer]);
        else if(mlen == 1){
            for(int i = 0; i < nlen; i++)
            result.add(matrix[layer][layer + i]);
        }
        else if(nlen == 1){
            for(int i = 0; i < mlen; i++)
            result.add(matrix[layer + i][layer]);
        }
        else{
            
            for(int i = 0; i < nlen - 1; i++)
                result.add(matrix[layer][layer + i]);
                
            for(int i = 0; i < mlen - 1; i++)
                result.add(matrix[layer + i][layer + nlen - 1]);
                
            for(int i = 0; i < nlen - 1; i++)
                result.add(matrix[layer + mlen - 1][layer + nlen - 1 - i]);
                
            for(int i = 0; i < mlen - 1; i++)
                result.add(matrix[layer + mlen - 1 - i][layer]);
        }
        spiralRecur(matrix, layer + 1, result, m ,n);
    }
}