Rotate Image Solution | Leetcode (In-place)

Introduction:

In this tutorial we will try to solve Rotate Image problem from Leetcode. it is an important question from coding interview point of view. so let's try to solve it.

Problem Statement:

We have give a n*n 2D matrix. and we have to rotate it by 90 degree in Clockwise direction.

Actually if you know little bit about Image Processing, then You already know that for manipulation or processing purpose we represent any image in the form of a 2D matrix. that's why the name of the problem is Rotate Image, which is quite relatable.

Given input matrix =
[
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
], 

Output:
[
  [15,13, 2, 5],
  [14, 3, 4, 1],
  [12, 6, 8, 9],
  [16, 7,10,11]
]

Solution:

whenever you find these type of problem related to 2D matrix. then think in this way.

In any 2D matrix there will be four corner points, leftTop, rightTop, leftDown, rightDown. so we have to keep track of these four points. and we need an extra variable which will keep track of when we will stop doing this or when we will stop our execution.

Full Code:

 void rotate(vector<vector<int>>& matrix) {
    int s=matrix.size()-1;
    int m=0;
    int j=s-m;
    while(m<j){
        int i=m,k=s-m,l=s-m;
    while(i<j){
        int temp=matrix[m][i];
        matrix[m][i]=matrix[l][m];
        int temp1=matrix[i][j];
        matrix[i][j]=temp;
        temp=matrix[k][l];
        matrix[k][l]=temp1;
        matrix[l][m]=temp;
        i++;
        l--;
    }
    m++;
    if(m>j){
        break;
    }
    j=s-m;
}
    }

In this solution I am using 5 variables m, i, j, k, l;

m = when we will go to next row and when we will stop execution.

i = it will keep track of uppermost row.

j = it will keep track of rightmost column.

k=it will keep track of lowermost row.

l=it will keep track of leftmost column.

do a dry run and then you will completely understand the code.

still if you have any query, just comment it down.