Spiral Matrix

public class Solution {
    public ArrayList<Integer> spiralOrder(int[][] matrix) {
        ArrayList<Integer> res = new ArrayList<Integer>();
        if(matrix==null || matrix.length==0 || matrix[0].length==0) return res;
        int bottom=matrix.length-1, top=0, left=0, right = matrix[0].length-1;
        while(left<right && top<bottom){
            for(int i=left;i<right;i++){
                res.add(matrix[top][i]);
            }
            for(int j=top;j<bottom;j++){
                res.add(matrix[j][right]);
            }
            for(int i=right;i>left;i--){
                res.add(matrix[bottom][i]);
            }
            for(int j=bottom;j>top;j--){
                res.add(matrix[j][left]);
            }
            right--;
            left++;
            top++;
            bottom--;
        }
        if(left==right){
            for(int i=top; i<=bottom; i++) res.add(matrix[i][left]);
        }else if(top==bottom){ // must be "else if" not "if"
            for(int j=left;j<=right;j++) res.add(matrix[top][j]);
        }
        return res;
    }
}

public class Solution {
    public int[][] generateMatrix(int n) {
        if(n<0) return null;
        int[][] res = new int[n][n];
        int r=n-1, l=0, t=0, b=n-1;
        int k=1;
        while(l<r){
            for(int i=l; i<r; i++){
                res[t][i] = k++;
            }
            for(int i=t; i<b; i++){
                res[i][r] = k++;
            }
            for(int i=r; i>l; i--){
                res[b][i] = k++;
            }
            for(int i=b; i>t; i--){
                res[i][l] = k++;
            }
            l++;
            r--;
            b--;
            t++;
        }
        if(n%2==1) res[(int) n/2][(int) n/2] = k++;
        return res;
    }
}