59. Spiral Matrix II.md

59. Spiral Matrix II

---

leetcode Daily Challenge on December 7th, 2020.

---

Difficulty : Medium

Related Topics : Array

---

Given a positive integer n, generate an n x n matrix filled with elements from 1 to n^2 in spiral order.

Example 1:

Input: n = 3
Output: [[1,2,3],[8,9,4],[7,6,5]]

Example 2:

Input: n = 1
Output: [[1]]

Constraints:

• 1 <= n <= 20

---

Solution

• mine
  • Java
    • Runtime: 0 ms, faster than 100.00%, Memory Usage: 38.4 MB, less than 5.05% of Java online submissions

      public int[][] generateMatrix(int n) {
          int[][] arr = {{0,1},{1,0},{0,-1},{-1,0}};
          int index = 0;
          int total = n * n;
          int x = 0, y = 0;
          int[][] res = new int[n][n];
          for(int i = 1; i <= total; i++){
              res[x][y] = i;
              int nextx = x + arr[index][0];
              int nexty = y + arr[index][1];
              if(nextx < 0 || nextx >= n || nexty < 0 || nexty >= n
                 || res[nextx][nexty] != 0){
                  index = (index + 1) % 4;
              }
              x += arr[index][0];
              y += arr[index][1];
          }
          return res;
      }
      

---