[LeetCode] 59. Spiral Matrix II

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

螺旋矩阵II。

题意是给一个数字n，请输出一个n x n的矩阵，被从1到n方这n方个数字填满。填满的方式同54题。

这个题跟54题做法几乎一样。也是要通过找到row和column的边界来完成填充的动作。首先创建一个n x n的二维数组并用0填满。遍历的时候，也是按照右 - 下 - 左 - 上的顺序。

时间O(n)

空间O(n^2)

JavaScript实现

/**
 * @param {number} n
 * @return {number[][]}
 */
var generateMatrix = function (n) {
    let res = Array(n).fill(0).map(() => Array(n).fill(0));
    let rowBegin = 0;
    let rowEnd = n - 1;
    let colBegin = 0;
    let colEnd = n - 1;
    let num = 1;

    while (rowBegin <= rowEnd && colBegin <= colEnd) {
        // right
        for (let i = colBegin; i <= colEnd; i++) {
            res[rowBegin][i] = num++;
        }
        rowBegin++;

        // down
        for (let i = rowBegin; i <= rowEnd; i++) {
            res[i][colEnd] = num++;
        }
        colEnd--;

        // left
        for (let i = colEnd; i >= colBegin; i--) {
            res[rowEnd][i] = num++;
        }
        rowEnd--;

        // up
        for (let i = rowEnd; i >= rowBegin; i--) {
            res[i][colBegin] = num++;
        }
        colBegin++;
    }
    return res;
};

Java实现

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        int rowBegin = 0;
        int rowEnd = n - 1;
        int colBegin = 0;
        int colEnd = n - 1;
        int num = 1;

        while (rowBegin <= rowEnd && colBegin <= colEnd) {
            for (int i = colBegin; i <= colEnd; i++) {
                matrix[rowBegin][i] = num++;
            }
            rowBegin++;

            for (int i = rowBegin; i <= rowEnd; i++) {
                matrix[i][colEnd] = num++;
            }
            colEnd--;

            for (int i = colEnd; i >= colBegin; i--) {
                matrix[rowEnd][i] = num++;
            }
            rowEnd--;

            for (int i = rowEnd; i >= rowBegin; i--) {
                matrix[i][colBegin] = num++;
            }
            colBegin++;
        }
        return matrix;
    }
}

LeetCode 题目总结