g0001_0100.s0059_spiral_matrix_ii.Solution Maven / Gradle / Ivy

Go to download
package g0001_0100.s0059_spiral_matrix_ii;

// #Medium #Array #Matrix #Simulation #Data_Structure_II_Day_3_Array
// #2022_06_17_Time_0_ms_(100.00%)_Space_42_MB_(47.35%)

/**
 * 59 - Spiral Matrix II\.
 *
 * Medium
 *
 * Given a positive integer `n`, generate an `n x n` `matrix` filled with elements from `1` to `n2` in spiral order.
 *
 * **Example 1:**
 *
 * ![](https://assets.leetcode.com/uploads/2020/11/13/spiraln.jpg)
 *
 * **Input:** n = 3
 *
 * **Output:** [[1,2,3],[8,9,4],[7,6,5]] 
 *
 * **Example 2:**
 *
 * **Input:** n = 1
 *
 * **Output:** [[1]] 
 *
 * **Constraints:**
 *
 * *   `1 <= n <= 20`
**/
public class Solution {
    public int[][] generateMatrix(int n) {
        int num = 1;
        int rStart = 0;
        int rEnd = n - 1;
        int cStart = 0;
        int cEnd = n - 1;
        int[][] spiral = new int[n][n];
        while (rStart <= rEnd && cStart <= cEnd) {
            for (int k = cStart; k <= cEnd; k++) {
                spiral[rStart][k] = num++;
            }
            rStart++;
            for (int k = rStart; k <= rEnd; k++) {
                spiral[k][cEnd] = num++;
            }
            cEnd--;
            if (rStart <= rEnd) {
                for (int k = cEnd; k >= cStart; k--) {
                    spiral[rEnd][k] = num++;
                }
            }
            rEnd--;
            if (cStart <= cEnd) {
                for (int k = rEnd; k >= rStart; k--) {
                    spiral[k][cStart] = num++;
                }
            }
            cStart++;
        }
        return spiral;
    }
}