Algorithm
Problem Name: 59. Spiral Matrix II
Problem Link: https://leetcode.com/problems/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
Code Examples
#1 Code Example with C Programming
Code -
C Programming
#include <stdio.h>
#include <stdlib.h>
int** generateMatrix(int n) {
int **matrix = (int **)malloc(n * sizeof(int *));
if (n == 0) return matrix;
int i;
for (i = 0; i < n; i++) {
matrix[i] = (int *)malloc(n * sizeof(int));
}
int left = 0;
int right = n - 1;
int up = 0;
int down = n - 1;
int k = 1;
while (left < = right && up <= down) {
if (left == right && up == down) {
matrix[left][up] = k++;
}
else {
for (i = left; i < = right - 1; i++)
matrix[up][i] = k++;
for (i = up; i < = down - 1; i++)
matrix[i][right] = k++;
for (i = right; i >= left + 1; i--)
matrix[down][i] = k++;
for (i = down; i >= up + 1; i--)
matrix[i][left] = k++;
}
left++;
right--;
up++;
down--;
}
return matrix;
}
int main() {
int n = 3;
int **m = generateMatrix(n);
int i, j;
for (i = 0; i < n; i++) {
for (j = 0; j < n; j++) {
printf("%d ", m[i][j]);
}
printf("\n");
}
return 0;
}
Input
n = 3
Output
[[1,2,3],[8,9,4],[7,6,5]]
#2 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
vector<vector<int>> generateMatrix(int n) {
vector < vector<int>>matrix(n, vector<int>(n, 0));
if(n == 0) return matrix;
spiral(matrix, 0, n - 1, 0, n - 1, 1, n);
return matrix;
}
void spiral(vector<vector < int>>& matrix, int minRow, int maxRow, int minCol, int maxCol, int k, int n>{
if(k > n * n) return;
if(k == n * n){
matrix[minRow][minCol] = k;
return;
}
for(int i = minCol; i <= maxCol; i++) matrix[minRow][i] = k++;
minRow++;
for(int i = minRow; i < = maxRow; i++> matrix[i][maxCol] = k++;
maxCol--;
for(int i = maxCol; i >= minCol; i--) matrix[maxRow][i] = k++;
maxRow--;
for(int i = maxRow; i >= minRow; i--) matrix[i][minCol] = k++;
minCol++;
spiral(matrix, minRow, maxRow, minCol, maxCol, k, n);
}
};
Input
1
Output
[[1]]
#3 Code Example with Java Programming
Code -
Java Programming
class Solution {
public int[][] generateMatrix(int n) {
int[][] ans = new int[n][n];
int left = 0;
int top = 0;
int right = n -1;
int down = n - 1;
int count = 1;
while (left < = right) {
for (int j = left; j <= right; j ++) {
ans[top][j] = count++;
}
top++;
for (int i = top; i < = down; i ++) {
ans[i][right] = count ++;
}
right--;
for (int j = right; j >= left; j --) {
ans[down][j] = count ++;
}
down--;
for (int i = down; i >= top; i --) {
ans[i][left] = count ++;
}
left++;
}
return ans;
}
}
Input
n = 3
Output
[[1,2,3],[8,9,4],[7,6,5]]
#4 Code Example with Javascript Programming
Code -
Javascript Programming
const generateMatrix = function(n) {
const res = [];
for (let i = 0; i < n; i++) {
res[i] = [];
}
let i = 0,
j = 0,
cur = 1;
while (n > 0) {
res[i][j] = cur++;
n--;
let step = n;
while (step > 0) {
res[i][++j] = cur++;
step--;
}
step = n;
while (step > 0) {
res[++i][j] = cur++;
step--;
}
step = n--;
while (step > 0) {
res[i][--j] = cur++;
step--;
}
step = n;
while (step > 0) {
res[--i][j] = cur++;
step--;
}
j++;
}
return res;
};
Input
n = 3
Output
[[1,2,3],[8,9,4],[7,6,5]]
#5 Code Example with Python Programming
Code -
Python Programming
class Solution:
def generateMatrix(self, n):
"""
:type n: int
:rtype: List[List[int]]
"""
def dirToIndex(x, y, d):
if d == "r": return (x, y + 1, d) if y + 1 < n and matrix[x][y + 1] == 0 else (x + 1, y, "d")
elif d == "d": return (x + 1, y, d) if x + 1 < n and matrix[x + 1][y] == 0 else (x, y - 1, "l")
elif d == "l": return (x, y - 1, d) if y > 0 and matrix[x][y - 1] == 0 else (x - 1, y, "u")
else: return (x - 1, y, d) if x > 0 and matrix[x - 1][y] == 0 else (x, y +1, "r")
matrix = [[0 for i in range(1, n + 1)] for j in range(n)]
num, dir, i, j = 1, "r", 0, 0
while 0 <= i < n and 0 <= j < n and matrix[i][j] == 0:
matrix[i][j] = num
num += 1
i, j, dir = dirToIndex(i, j, dir)
return matrix
Input
n = 3
Output
[[1,2,3],[8,9,4],[7,6,5]]
#6 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _059_SpiralMatrix2
{
public int[,] GenerateMatrix(int n)
{
var result = new int[n, n];
int start = 0, end = n - 1;
int num = 1, i;
while (start < end)
{
for (i = start; i < end; i++) result[start, i] = num++;
for (i = start; i < end; i++) result[i, end] = num++;
for (i = end; i > start; i--) result[end, i] = num++;
for (i = end; i > start; i--) result[i, start] = num++;
start++;
end--;
}
if (start == end) result[start, start] = num;
return result;
}
}
}
Input
n = 3
Output
[[1,2,3],[8,9,4],[7,6,5]]