Rotate Matrix Counterclockwise by 1
Last Updated :
18 Oct, 2024
Given a square matrix, the task is to rotate its elements counterclockwise by one step.
Examples:
Input
1 2 3
4 5 6
7 8 9
Output:
2 3 6
1 5 9
4 7 8
Input:
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
Output:
2 3 4 8
1 7 11 12
5 6 10 16
9 13 14 15
The idea is to use nested loops to move elements in four directions (right, down, left, and up) one step at a time for each layer starting from the outermost layer. This simulates the clockwise rotation by rotating each "ring" or layer of the matrix.
1. First move the elements of the outermost layer.
a) Move the top row elements one position back (except the first element)
b) Move the rightmost column elements one position up (except the first element)
c) Move the bottom row elements one position right (Except the rightmost element)
d) Move the first column elements one position down (Except the bottom elements)
2. Repeat the same process for inner layers.
C++
#include <bits/stdc++.h>
using namespace std;
// Function to rotate a matrix counterclockwise
void rotateMatrix(vector<vector<int>>& mat) {
int m = mat.size();
int n = mat[0].size();
int row = 0, col = 0;
int prev, curr;
// Rotate the matrix in layers
while (row < m && col < n) {
if (row + 1 == m || col + 1 == n)
break;
// Store the first element of the next column
prev = mat[row][col + 1];
// Move elements of the first column
for (int i = row; i < m; i++) {
curr = mat[i][col];
mat[i][col] = prev;
prev = curr;
}
col++;
// Move elements of the last row
for (int i = col; i < n; i++) {
curr = mat[m - 1][i];
mat[m - 1][i] = prev;
prev = curr;
}
m--;
// Move elements of the last column
if (col < n) {
for (int i = m - 1; i >= row; i--) {
curr = mat[i][n - 1];
mat[i][n - 1] = prev;
prev = curr;
}
}
n--;
// Move elements of the first row
if (row < m) {
for (int i = n - 1; i >= col; i--) {
curr = mat[row][i];
mat[row][i] = prev;
prev = curr;
}
}
row++;
}
}
int main() {
vector<vector<int>> mat = {
{1, 2, 3, 4},
{5, 6, 7, 8},
{9, 10, 11, 12},
{13, 14, 15, 16}
};
rotateMatrix(mat);
// Print the rotated matrix
for (auto& r : mat) {
for (int val : r)
cout << val << " ";
cout << endl;
}
return 0;
}
import java.util.Arrays;
class GfG {
// Function to rotate a matrix counterclockwise
static void rotateMatrix(int[][] mat) {
int m = mat.length;
int n = mat[0].length;
int row = 0, col = 0;
int prev, curr;
// Rotate the matrix in layers
while (row < m && col < n) {
if (row + 1 == m || col + 1 == n)
break;
// Store the first element of the next column
prev = mat[row][col + 1];
// Move elements of the first column
for (int i = row; i < m; i++) {
curr = mat[i][col];
mat[i][col] = prev;
prev = curr;
}
col++;
// Move elements of the last row
for (int i = col; i < n; i++) {
curr = mat[m - 1][i];
mat[m - 1][i] = prev;
prev = curr;
}
m--;
// Move elements of the last column
if (col < n) {
for (int i = m - 1; i >= row; i--) {
curr = mat[i][n - 1];
mat[i][n - 1] = prev;
prev = curr;
}
}
n--;
// Move elements of the first row
if (row < m) {
for (int i = n - 1; i >= col; i--) {
curr = mat[row][i];
mat[row][i] = prev;
prev = curr;
}
}
row++;
}
}
public static void main(String[] args) {
int[][] mat = {
{1, 2, 3, 4},
{5, 6, 7, 8},
{9, 10, 11, 12},
{13, 14, 15, 16}
};
rotateMatrix(mat);
// Print the rotated matrix
for (int[] r : mat) {
for (int val : r)
System.out.print(val + " ");
System.out.println();
}
}
}
def rotateMatrix(mat):
# Function to rotate a matrix counterclockwise
m = len(mat)
n = len(mat[0])
row = 0
col = 0
prev = 0
curr = 0
# Rotate the matrix in layers
while row < m and col < n:
if row + 1 == m or col + 1 == n:
break
# Store the first element of the next column
prev = mat[row][col + 1]
# Move elements of the first column
for i in range(row, m):
curr = mat[i][col]
mat[i][col] = prev
prev = curr
col += 1
# Move elements of the last row
for i in range(col, n):
curr = mat[m - 1][i]
mat[m - 1][i] = prev
prev = curr
m -= 1
# Move elements of the last column
if col < n:
for i in range(m - 1, row - 1, -1):
curr = mat[i][n - 1]
mat[i][n - 1] = prev
prev = curr
n -= 1
# Move elements of the first row
if row < m:
for i in range(n - 1, col - 1, -1):
curr = mat[row][i]
mat[row][i] = prev
prev = curr
row += 1
if __name__ == "__main__":
mat = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16]
]
rotateMatrix(mat)
for r in mat:
print(" ".join(map(str, r)))
using System;
class GfG {
// Function to rotate a matrix counterclockwise
static void rotateMatrix(int[][] mat) {
int m = mat.Length;
int n = mat[0].Length;
int row = 0, col = 0;
int prev, curr;
// Rotate the matrix in layers
while (row < m && col < n) {
if (row + 1 == m || col + 1 == n)
break;
// Store the first element of the next column
prev = mat[row][col + 1];
// Move elements of the first column
for (int i = row; i < m; i++) {
curr = mat[i][col];
mat[i][col] = prev;
prev = curr;
}
col++;
// Move elements of the last row
for (int i = col; i < n; i++) {
curr = mat[m - 1][i];
mat[m - 1][i] = prev;
prev = curr;
}
m--;
// Move elements of the last column
if (col < n) {
for (int i = m - 1; i >= row; i--) {
curr = mat[i][n - 1];
mat[i][n - 1] = prev;
prev = curr;
}
}
n--;
// Move elements of the first row
if (row < m) {
for (int i = n - 1; i >= col; i--) {
curr = mat[row][i];
mat[row][i] = prev;
prev = curr;
}
}
row++;
}
}
static void Main() {
int[][] mat = {
new int[] {1, 2, 3, 4},
new int[] {5, 6, 7, 8},
new int[] {9, 10, 11, 12},
new int[] {13, 14, 15, 16}
};
rotateMatrix(mat);
// Print the rotated matrix
foreach (var r in mat) {
foreach (int val in r)
Console.Write(val + " ");
Console.WriteLine();
}
}
}
function rotateMatrix(mat) {
// Function to rotate a matrix counterclockwise
let m = mat.length;
let n = mat[0].length;
let row = 0, col = 0;
let prev, curr;
// Rotate the matrix in layers
while (row < m && col < n) {
if (row + 1 === m || col + 1 === n) break;
// Store the first element of the next column
prev = mat[row][col + 1];
// Move elements of the first column
for (let i = row; i < m; i++) {
curr = mat[i][col];
mat[i][col] = prev;
prev = curr;
}
col++;
// Move elements of the last row
for (let i = col; i < n; i++) {
curr = mat[m - 1][i];
mat[m - 1][i] = prev;
prev = curr;
}
m--;
// Move elements of the last column
if (col < n) {
for (let i = m - 1; i >= row; i--) {
curr = mat[i][n - 1];
mat[i][n - 1] = prev;
prev = curr;
}
}
n--;
// Move elements of the first row
if (row < m) {
for (let i = n - 1; i >= col; i--) {
curr = mat[row][i];
mat[row][i] = prev;
prev = curr;
}
}
row++;
}
}
const mat = [
[1, 2, 3, 4],
[5, 6, 7, 8],
[9, 10, 11, 12],
[13, 14, 15, 16]
];
rotateMatrix(mat);
mat.forEach(r => {
console.log(r.join(" "));
});
Output2 3 4 8
1 7 11 12
5 6 10 16
9 13 14 15
Time Complexity: O(m*n) where m is the number of rows & n is the number of columns.
Auxiliary Space: O(1).
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