LeetCode 59. Spiral Matrix II

Question

Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order.

https://leetcode.com/problems/spiral-matrix-ii/

• Solution1

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        if (n <= 0) return res;
        int top = 0, bottom = n - 1;
        int left = 0, right = n - 1;
        int k = 1;
        while (top < bottom && left < right) {
            for (int i = left; i < right; i++) res[top][i] = k++;
            for (int i = top; i < bottom; i++) res[i][right] = k++;
            for (int i = right; i > left; i--) res[bottom][i] = k++;
            for (int i = bottom; i > top; i--) res[i][left] = k++;
            top++;
            bottom--;
            left++;
            right--;
        }
        if (n %2 != 0) res[n / 2][n / 2] = k;
        return res;
    }
}

Complexity:

Time complexity: O(mn)

Space complexity: O(mn)