59. 螺旋矩阵 II

59. 螺旋矩阵 II

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        int start = 0;
        int startNum = 1;
        while (2 * start < n) {
            int endX = n - 1 - start;
            int endY = n - 1 - start;
            for (int i = start; i <= endX; i++) {
                matrix[start][i] = startNum++; 
            }
            if (start < endY) {
                for (int i = start + 1; i <= endY; i++) {
                    matrix[i][endX] = startNum++;
                }
            }
            if (start < endX && start < endY) {
                for (int i = endY - 1; i >= start; i--) {
                    matrix[endY][i] = startNum++;
                }
            }
            if (start < endX && start < endY - 1) {
                for (int i = endX - 1; i >= start + 1; i--) {
                    matrix[i][start] = startNum++;
                }
            }
            ++start;
        }
        return matrix;
    }
}