Spiral Matrix

details kill 

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;

    }

}

 II

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;

    }

}