54. Spiral Matrix/59. Spiral Matrix II

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new LinkedList<>();
        if (matrix.length == 0 || matrix[0].length == 0) {
            return res;
        }
        int top = 0;
        int left = 0;
        int bottom = matrix.length - 1;
        int right = matrix[0].length - 1;
        while (left < right && top < bottom) {
            for (int i = left; i < right; i++) {
                res.add(matrix[top][i]);
            }
            for (int i = top; i < bottom; i++) {
                res.add(matrix[i][right]);
            }
            for (int i = right; i > left; i--) {
                res.add(matrix[bottom][i]);
            }
            for (int i = bottom; i > top; i--) {
                res.add(matrix[i][left]);
            }
            top ++;
            left ++;
            bottom --;
            right --;
        }
        
        if (left == right) {
            for (int i = top; i <= bottom; i++) {
                res.add(matrix[i][left]);
            }            
        } else if (top == bottom) {
            for (int i = left; i <= right; i++) {
                res.add(matrix[top][i]);
            }
        }
        
        return res;
    }
}

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        int left = 0; 
        int top = 0;
        int right = n - 1;
        int bottom = n - 1;
        int j = 1;
        while (left < right) {
            for (int i = left; i < right; i++) {
                matrix[top][i] = j++;
            }
            for (int i = top; i < bottom; i++) {
                matrix[i][right] = j++;
            }
            for (int i = right; i > left; i--) {
                matrix[bottom][i] = j++;
            }
            for (int i = bottom; i > top; i--) {
                matrix[i][left] = j++;
            }
            left ++;
            top ++;
            right --;
            bottom --;
        }
        if (left == right) {
            matrix[top][left] = j;
        }
        return matrix;
    }
}