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Program to print Sum Triangle for a given array
  • Difficulty Level : Easy
  • Last Updated : 21 May, 2021

Given a array, write a program to construct a triangle where last row contains elements of given array, every element of second last row contains sum of below two elements and so on.

Example: 

Input: arr[] = {4, 7, 3, 6, 7};
Output:
81
40 41
21 19 22
11 10 9 13
4 7 3 6 7 

Input: {10, 40, 50}
Output:
140
50 90
10 40 50

An important observation about output is final value is at the top and top element needs to printed first. Therefore, we use a 2D auxiliary array to construct the triangle in bottom up manner and then print the triangle. An element tri[i][j] of 2D array can be calculated as sum of tri[i+1][j] and tri[i+1][j+1].

Below is the implementation of above idea : 

C++




// C++ program to print sum triangle for a given array
#include <bits/stdc++.h>
using namespace std;
 
// prints sum triangle for arr[0..n-1]
void printTriangle(int arr[], int n)
{
    // Initialize a 2D array to store triangle
    int tri[n][n];
    memset(tri, 0, sizeof(tri));
 
    // Initialize last row of triangle
    for (int i = 0; i < n ; i++)
        tri[n-1][i] = arr[i];
 
    // Fill other rows
    for (int i = n-2; i >=0; i--)
      for (int j = 0; j <= i; j++)
        tri[i][j] = tri[i+1][j] + tri[i+1][j+1];
 
    // Print the triangle
    for (int i = 0; i < n; i++)
    {
        for(int j = 0; j <= i ; j++)
            cout << tri[i][j]<<" ";
        cout << endl;
    }
}
 
// Driver Program
int main()
{
    int arr[] = {4, 7, 3, 6, 7};
    int n = sizeof(arr)/sizeof(arr[0]);
    printTriangle(arr, n);
    return 0;
}

Java




// Java program to print sum triangle for a given array
class Test{
      
     static int arr[] = new int[]{4, 7, 3, 6, 7};
      
     // prints sum triangle for arr[0..n-1]
     public static void printTriangle(int n)
     {
        // Initialize a 2D array to store triangle
        int tri[][] = new int[n][n];
          
        // Initialize last row of triangle
        for (int i = 0; i < n ; i++)
            tri[n-1][i] = arr[i];
          
        // Fill other rows
        for (int i = n-2; i >=0; i--)
            for (int j = 0; j <= i; j++)
               tri[i][j] = tri[i+1][j] + tri[i+1][j+1];
          
        // Print the triangle
        for (int i = 0; i < n; i++)
        {
            for(int j = 0; j <= i ; j++)
                System.out.print(tri[i][j] + " ");
            System.out.println();
        }
     }
      
     public static void main(String[] args)
     {
         printTriangle(arr.length);
        }
 }

Python3




# Python 3 program to print sum triangle
# for a given array
 
# prints sum triangle for arr[0..n-1]
def printTriangle(arr, n):
     
    # Initialize a 2D array to store triangle
    tri = [[0 for i in range(n)]
              for i in range(n)]
 
    # Initialize last row of triangle
    for i in range(n):
        tri[n - 1][i] = arr[i]
 
    # Fill other rows
    i = n - 2
    while(i >= 0):
        for j in range(0, i + 1, 1):
            tri[i][j] = (tri[i + 1][j] +
                         tri[i + 1][j + 1])
             
        i -= 1
 
    # Print the triangle
    for i in range(0, n, 1):
        for j in range(0, i + 1, 1):
            print(tri[i][j], end = " ")
        print("\n", end = "")
 
# Driver Code
if __name__ == '__main__':
    arr = [4, 7, 3, 6, 7]
    n = len(arr)
    printTriangle(arr, n)
     
# This code is contributed by
# Shashank_Sharma

C#




// C# program to print sum triangle
// for a given array
using System;
 
class GFG {
     
    static int []arr = new int[]{4, 7, 3, 6, 7};
     
    // prints sum triangle for arr[0..n-1]
    public static void printTriangle(int n)
    {
        // Initialize a 2D array to store triangle
        int [,]tri = new int[n, n];
         
        // Initialize last row of triangle
        for (int i = 0; i < n ; i++)
            tri[n - 1, i] = arr[i];
         
        // Fill other rows
        for (int i = n - 2; i >= 0; i--)
            for (int j = 0; j <= i; j++)
            tri[i, j] = tri[i + 1, j] +
                        tri[i + 1, j + 1];
          
        // Print the triangle
        for (int i = 0; i < n; i++)
        {
            for(int j = 0; j <= i ; j++)
                Console.Write(tri[i, j] + " ");
                Console.WriteLine();
        }
    }
     
    // Driver Code
    public static void Main()
    {
        printTriangle(arr.Length);
    }
}
 
// This code is contributed by Sam007.

PHP




<?php
// PHP program to print sum
// triangle for a given array
 
// prints sum triangle for arr[0..n-1]
function printTriangle($arr, $n)
{
    // Initialize a 2D array to store triangle
    $tri[$n][$n] = array(array());
    array_fill(0, count($tri), 0);
 
    // Initialize last row of triangle
    for ($i = 0; $i < $n ; $i++)
        $tri[$n - 1][$i] = $arr[$i];
 
    // Fill other rows
    for ($i = $n - 2; $i >= 0; $i--)
    for ($j = 0; $j <= $i; $j++)
        $tri[$i][$j] = $tri[$i + 1][$j] +
                       $tri[$i + 1][$j + 1];
 
    // Print the triangle
    for ($i = 0; $i < $n; $i++)
    {
        for( $j = 0; $j <= $i ; $j++)
            echo $tri[$i][$j] . " ";
        echo "\n";
    }
}
 
// Driver Code
$arr = array(4, 7, 3, 6, 7);
$n = count($arr);
printTriangle($arr, $n);
 
// This code is contributed by Rajput-Ji
?>

Javascript




<script>
      // JavaScript program to print sum triangle for a given array
 
      // prints sum triangle for arr[0..n-1]
      function printTriangle(arr, n)
      {
       
        // Initialize a 2D array to store triangle
        var tri = new Array(n).fill(0).map((item) => new Array(n).fill(0));
 
        // Initialize last row of triangle
        for (var i = 0; i < n; i++) tri[n - 1][i] = arr[i];
 
        // Fill other rows
        for (var i = n - 2; i >= 0; i--)
          for (var j = 0; j <= i; j++)
            tri[i][j] = tri[i + 1][j] + tri[i + 1][j + 1];
 
        // Print the triangle
        for (var i = 0; i < n; i++) {
          for (var j = 0; j <= i; j++)
            document.write(tri[i][j] + "  ");
          document.write("<br>");
        }
      }
 
      // Driver Program
      var arr = [4, 7, 3, 6, 7];
      var n = arr.length;
      printTriangle(arr, n);
       
      // This code is contributed by rdtank.
    </script>

Output: 



81
40 41
21 19 22
11 10 9 13
4 7 3 6 7
 

Thanks to nish for suggesting this solution.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
 

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