How to print Pascal's Triangle by given index | Pascal's Triangle II LeetCode Solution

Pascal's Triangle II LeetCode Solution in Java

Problem description :

Return particular row index of Pascal's Triangle based on given index.

Sample input and output :

Input 1 :
4

Output 1 :
[1, 4, 6, 4, 1]

Input 2 :
7

Output 2 :
[1, 7, 21, 35, 35, 21, 7, 1]

In Pascal's triangle, each number is the sum of the two numbers directly above. You can see in above image.

Lets see solution.

Solution 1 : Using Java List

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class PascalsTriangle {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.println("Enter row");
        int row = sc.nextInt();
        int[] array = new int[row];
        print(row);
    }
    
    public static void print(int row) {

        List<Integer> list = new ArrayList<>();
        for (int i = 0; i <= row; i++) {
            list.add(1);
            for (int j = i-1; j > 0; j--) {
                list.set(j, list.get(j) + list.get(j-1));
            }
        }
        System.out.println(list);
    }

}

Output :

Enter row
4
[1, 4, 6, 4, 1]

Enter row
10
[1, 10, 45, 120, 210, 252, 210, 120, 45, 10, 1]

Output explanation :

• row = 4, i = 0, 0 <= 4 becomes true
  
• list.add(1) | list = [1]
• j = -1, -1 > 0 becomes false
  
  
• i = 1
  
• list.add(1) | list = [1, 1]
• j = 0, 0 > 0 becomes false
  
  
• i = 2
• list.add(1) | list = [1, 1, 1]
• j = 1, 1 > 0 becomes true
• list.set(1, list.get(1) + list.get(1-1)) | list.set(1, 2) | set 2 at index 1
• list = [1, 2, 1]
  
  
• i = 3
• list.add(1) | list = [1, 2, 1, 1]
• j = 2, 2 > 0 becomes true
• list.set(2, 3) | set 3 at index 2
• list = [1, 2, 3, 1]
• j = 1, 1 > 0 becomes true 
• list.set(1, 3) | set 3 at index 1
• list = [1, 3, 3, 1]
  
  
• i = 4
• list.add(1) | list = [1, 3, 3, 1, 1]
• j = 3, 3 > 0 becomes true
• list.set(3, 4) | set 4 at index 3
• list = [1, 3, 3, 4, 1]
• j = 2, 2 > 0 becomes true 
• list.set(2, 5) | set 6 at index 2
• list = [1, 3, 6, 4, 1]
• j = 1, 1 > 0 becomes true 
• list.set(1, 4) | set 4 at index 1
• list = [1, 4, 6, 4, 1]
• j = 0, 0 > 0 becomes false.
• i = 5, 5 >= 4 becomes false
• Print or return list = [1, 4, 6, 4, 1]

Solution 2 : Using Java Array

    public static void print(int row) {
        Integer[] array = new Integer[row + 1];
        Arrays.fill(array, 0);
        array[0] = 1;
       
        for (int i = 1; i <= row; i++) {
            for (int j = i; j > 0; j--) {
                array[j] = array[j] + array[j-1];
            }
        }
       
        System.out.println(Arrays.asList(array));
    }

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