【leetcode】59. spiral matrix ii

public static int[][] generateMatrix(int n) {
    int[][] ret = new int[n][n];
    int left = 0,top = 0;
    int right = n -1,down = n - 1;
    int count = 1;
    while (left <= right) {

        for (int j = left; j <= right; j++) {
            ret[top][j] = count++;
        }
        top++;

        for (int i = top; i <= down; i++) {
            ret[i][right] = count++;
        }
        right--;

        for (int j = right; j >= left; j--) {
            ret[down][j] = count++;
        }
        down--;

        for (int i = down; i >= top; i--) {
            ret[i][left] = count++;
        }
        left++;
    }
    return ret;
}