Limited Time Offer:30% off Hello Interview Premium 🎉

Back to Main

Your Dashboard

Learn Code

Introduction

Two Pointers

Overview

Container With Most Water

Two Sum (Sorted Array)

3-Sum

Triangle Numbers

Move Zeroes

Sort Colors

Trapping Rain Water

Sliding Window

Overview

Longest Substring Without Repeating Characters

Longest Repeating Character Replacement

Overview

Maximum Sum of Subarrays of Size K

Max Points You Can Obtain From Cards

Max Sum of Distinct Subarrays Length k

Intervals

Overview

Can Attend Meetings

Insert Interval

Non-Overlapping Intervals

Merge Intervals

Employee Free Time

Stack

Overview

Valid Parentheses

Decode String

Longest Valid Parentheses

Overview

Daily Temperatures

Largest Rectangle in Histogram

Linked List

Overview

Linked List Cycle

Palindrome Linked List

Remove Nth Node From End of List

Reorder List

Swap Nodes in Pairs

Binary Search

Overview

Apple Harvest (Koko Eating Bananas)

Search in Rotated Sorted Array

Heap

Overview

Kth Largest Element in an Array

K Closest Points to Origin

Find K Closest Elements

Merge K Sorted Lists

Breadth-First Search

Introduction

Overview

Level Order Sum

Rightmost Node

Zigzag Level Order

Maximum Width of Binary Tree

Graphs Overview

Minimum Knight Moves

Rotting Oranges

01-Matrix

Bus Routes

Backtracking

Overview

Word Search

Solution Space Trees

Subsets

Generate Parentheses

Combination Sum

Graphs

Overview

Course Schedule

Course Schedule II

Dynamic Programming

Fundamentals

Solving a Question with Dynamic Programming

Counting Bits

Decode Ways

Maximal Square

Unique Paths

Longest Increasing Subsequence

Word Break

Maximum Profit in Job Scheduling

Greedy Algorithms

Overview

Best Time to Buy and Sell Stock

Gas Station

Jump Game

Trie

Overview

Implement Trie Methods

Prefix Matching

Prefix Sum

Overview

Count Vowels in Substrings

Subarray Sum Equals K

Matrices

Spiral Matrix

Rotate Image

Set Matrix Zeroes

Pricing

Become a Coach

⌘K

Pricing Become a Coach

⌘K

Get Premium

Matrices

Rotate Image

medium

DESCRIPTION (credit Leetcode.com)

Write a function to rotate an n x n 2D matrix representing an image by 90 degrees clockwise. The rotation must be done in-place, meaning you should modify the input matrix directly without using an additional matrix for the operation.

Input:


matrix = [
    [1,4,7],
    [2,5,8],
    [3,6,9]
]

Output:


[
    [3,2,1],
    [6,5,4],
    [9,8,7]
]

Explanation: The matrix is rotated by 90 degrees clockwise, transforming its columns into rows in reverse order.

Explanation

This problem can be done in two steps. We first transpose the matrix, then reverse the elements in each row.

Step 1:

Transpose the matrix by swapping the elements across the diagonal. This can be done in-place by using a nested for loop to swap the elements.


def rotate_image(matrix):
    n = len(matrix)

    # Transpose the matrix
    for i in range(n):
        for j in range(i, n):
            matrix[i][j], matrix[j][i] = \
                matrix[j][i], matrix[i][j]

    # Reverse each row
    for i in range(n):
        matrix[i] = matrix[i][::-1]
    return matrix

n = 3

0 / 12

Step 2:

Reverse the elements in each row of the matrix.


def rotate_image(matrix):
    n = len(matrix)

    # Transpose the matrix
    for i in range(n):
        for j in range(i, n):
            matrix[i][j], matrix[j][i] = \
                matrix[j][i], matrix[i][j]

    # Reverse each row
    for i in range(n):
        matrix[i] = matrix[i][::-1]
    return matrix

swap matrix[2][2] and matrix[2][2]

0 / 4

Solution


def rotate_image(matrix):
    n = len(matrix)

    # Transpose the matrix
    for i in range(n):
        for j in range(i, n):
            matrix[i][j], matrix[j][i] = \
                matrix[j][i], matrix[i][j]

    # Reverse each row
    for i in range(n):
        matrix[i] = matrix[i][::-1]
    return matrix

rotate image

0 / 17

Test Your Knowledge

Complexity Analysis

Time Complexity: O(n²) where n is the number of rows in the matrix. We need to process each element in the matrix.

Space Complexity: O(1) since we are doing the rotation in-place without using extra space.

Mark as read

Your account is free and you can post anonymously if you choose.

Matrices

Rotate Image

DESCRIPTION (credit Leetcode.com)

Explanation

Step 1:

Step 2:

Solution

Test Your Knowledge

Complexity Analysis

Questions

Learn

Links

Legal

Contact