Spiral Order Matrix II - The Coding Shala

Home >> Interview Questions >> Spiral Order matrix 2

Spiral Order Matrix II Problem Solution

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
Spiral Order Matrix 2 - The Coding Shala
Example:
Given n = 3,
You should return the following matrix:
[
  [ 1, 2, 3 ],
  [ 8, 9, 4 ],
  [ 7, 6, 5 ]
]

Solution: (Java)

The concept is the same as how to print the Spiral Order Matrix.

Approach:
Let's see for n= 4, then numbers will come from 1 to 16(n*n) in the matrix.
Spiral Order Matrix Explanation - The Coding Shala
As we need to insert numbers in spiral order so here we need 4 things to check, first and last column and top and bottom row. The following four steps we need to do:
  1. First, we need to insert numbers in the top row. Our loop will go from the left column to the right then will increase the top row by one and now the top is our second row.
  2. Now we are inserting the numbers in the right column, will start the loop from top to bottom, and then decrease the value of the right column by one. Now our right column is n-1 and so on later steps.
  3. Now insert the numbers in the bottom row. the loop will go from right to left and then decrease the value of the bottom. the bottom will go up.
  4. The last step is to insert the number in the left column. Loop will go from bottom to top row and then increase the value of the left column by one.
Once we follow all the above steps(one time) our outer layer is done all the left, right, top, bottom value updated. Follow these steps until left<=right and top<=bottom(outer loop).

Java Program:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
public class Solution {
    public ArrayList<ArrayList<Integer>> generateMatrix(int A) {
        int[][] res = new int[A][A];
        int left=0,right=A-1,top=0,bottom=A-1,num=1;
         //outer condition
        while(left<=right && top<=bottom){
          //for top row
            for(int i=left;i<=right;i++)
                res[top][i] = num++;
            top++;
            //for right column
            for(int i=top;i<=bottom;i++)
                res[i][right] = num++;
            right--;
            // for bottom row
            for(int i=right;i>=left;i--)
                res[bottom][i] = num++;
            bottom--;
            // for left column
            for(int i=bottom;i>=top;i--)
                res[i][left] = num++;
            left++;
        }
       // insert data from 2-d array to arraylist
        ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();
        for(int i=0;i<A;i++){
            ArrayList<Integer> tmp = new ArrayList<Integer>();
            for(int j=0;j<A;j++){
                tmp.add(res[i][j]);
            }
            ans.add(tmp);
        }
        return ans;
    }
}



Other Posts You May Like
Please leave a comment below if you like this post or found some error, it will help me to improve my content.
By

Comments

  1. Nisha KhandelwalSeptember 12, 2020 at 10:42 PM

    Could you explain the code with example please
    Thank you in advance

    ReplyDelete
    Replies
    1. Akshay KumarSeptember 14, 2020 at 6:48 PM

      Hi, added Approach and comments in the code. Please check now.

      Delete

Post a Comment

Popular Posts from this Blog

Java Program to Convert Binary to Decimal - The Coding Shala

Home >> Java Programs >> Convert Binary to Decimal  Hey there, welcome back to another post. In this post, we will learn how to convert Binary to Decimal in Java. Java Program to Convert Binary to Decimal You have given a binary number, convert it to a decimal number. Example:  Input: 101 Output: 5 Input: 111 Output: 7 Binary to Decimal Conversion in Java Approach We will the below formula to convert binary to decimal: decimal number = (2^0) * (rightmost digit) + (2^1) * (second rightmost digit) + ...  for example:  binary number = 110 decimal number = 2^0 * 0 + 2^1 * 1 + 2^2 * 1 = 1 * 0 + 2 * 1 + 4 * 1 = 0 + 2 + 4 = 6 Java Program:  import java.util.Scanner; /** * https://www.thecodingshala.com/ */ public class Main { public static void printDecimal( int num) { int decimal = 0; int twos = 1; // 2^0 = 1 initial value while (num > 0) { int temp = num
Read more

N-th Tribonacci Number Solution - The Coding Shala

Home >> Programming >> N-th Tribonacci Number  Hey there, welcome back to another post. In this post, we will learn how to solve the N-th Tribonacci Number problem and will implement its solution in Java. N-th Tribonacci Number Problem Statement The Tribonacci sequence Tn is defined as follows: T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0. Given n, return the value of Tn.  Example 1:  Input: n = 4 Output: 4 Explanation: T_3 = 0 + 1 + 1 = 2 T_4 = 1 + 1 + 2 = 4 N-th Tribonacci Number Java Solution using Bottom-Up DP This problem is similar to the Fibonacci series. We can solve it using the Bottom-Up approach of dynamic programming. Time Complexity: O(n) Space Complexity: O(n) The space complexity can be reduced to O(1) by using variables to store the previous three values instead of using an array. Java Program:  class Solution { public int tribonacci( int n) { if (n == 0) return 0; if (n == 1 || n == 2
Read more

Shell Script to find sum, product and average of given numbers - The Coding Shala

Home >> Scripting >> Sum, product and average Shell Script to find the sum, product, and the average of given numbers Read four integer numbers from the user and find the sum, product, and average of these four numbers? Code:  #! / bin / bash echo "enter four integers" read a b c d sum =$(echo "$a + $b + $c + $d" | bc - l) average=$(echo "$sum / 4" | bc - l) product=$(echo "$a * $b * $c * $d" | bc - l) echo "sum = $sum" echo "Average = $average" echo "Product = $product" Other Posts You May Like Shell script to print sum of the digits of a number Shell Script to print number in descending order Shell script to find out biggest number from three numbers Shell script to find out factorial of a number Shell Script to create a simple calculator Please leave a comment below if you like this post or found some error, it will help me to improve my content.
Read more

Shell Script to Create a Simple Calculator - The Coding Shala

Home >> Scripting >> simple calculator Shell Script to Create a Simple Calculator Write a shell script to create a simple calculator using a switch-case statement? Code:  #! / bin / bash echo "simple calculator" sum = 0 i = "y" echo "enter first number" read n1 echo "enter second number" read n2 while [ $ i = "y" ] do echo "1.Addition" echo "2.Subtraction" echo "3.Multiplication" echo "4.Division" echo "Enter choice" read ch case $ch in 1 ) sum =$(echo " $n1 + $n2" | bc - l) echo "Addition is =" $ sum ;; 2 ) sum =$(echo "$n1 - $n2" | bc - l) echo "Sub is =" $ sum ;; 3 ) sum =$(echo "$n1 * $n2" | bc - l) echo "Mul is =" $ sum ;; 4 ) sum =$(echo "$n1 / $n2" | bc - l) echo "div is =" $ sum ;; * )echo "invalid choice" esac echo "Do y
Read more

Java Program to Convert Decimal to Binary - The Coding Shala

Home >> Java Programs >> Convert Decimal to Binary  Hey there, welcome back to another post. In this post, we will learn how to convert decimal to binary in Java. Java Program to Convert Decimal to Binary You have given a decimal number. Write a Java program to convert decimal to binary. Example 1:  Input: 7 Output: 111 Input: 10 Output: 1010 Decimal to Binary Conversion using Array Approach To convert decimal to binary we can follow the below steps: Store the remainder in the array when we divide the number by 2. Divide the number by 2. Follow the above two steps until the number is above 0. Print the array in reverse order. For example:  4 % 2 = 0 => 4/2 = 2 2 % 2 = 0 => 2/2 = 1 1 % 2 = 1 => 1/2 = 0 Binary of 4 is: 100 Java Program:  import java.util.ArrayList; import java.util.List; import java.util.Scanner; /** * https://www.thecodingshala.com/ */ public class Main { public static void printBinary( int num) {
Read more