Construct sum-array with sum of elements in given range

You are given an array of n-elements and an odd-integer m. You have to construct a new sum_array from given array such that sum_array[i] = ?arr[j] for (i-(m/2)) < j (i+(m/2)). 

note : for 0 > j or j >= n take arr[j] = 0.

Examples: 

Input : arr[] = {1, 2, 3, 4, 5}, 
            m = 3
Output : sum_array = {3, 6, 9, 12, 9}
Explanation : sum_array[0] = arr[0] + arr[1]
     sum_array[1] = arr[0] + arr[1] + arr[2]
     sum_array[2] = arr[1] + arr[2] + arr[3]
     sum_array[3] = arr[2] + arr[3] + arr[4]
     sum_array[4] = arr[3] + arr[4]

Input : arr[] = {2, 4, 3, 4, 2}, 
           m = 1
Output : sum_array = {2, 4, 3, 4, 2}
Explanation : sum_array[0] = arr[0] 
              sum_array[1] = arr[1]
              sum_array[2] = arr[2]
              sum_array[3] = arr[3]
              sum_array[4] = arr[4]

Basic Approach : As per problem statement, we calculate sum_array[i] by iterating over i-(m/2) to i+(m/2). According to this approach, we have a nested loop which will result into time complexity of O(n*m).
Efficient Approach : For calculating sum_array is to use sliding window concept and thus can easily save our time. For Sliding window, the time complexity is O(n). 

Algorithm 

calculate sum of first (m/2)+1 elementssum_array[0] = sumfor i=1 to i<nif( (i-(m/2)-1) >= 0 )
           sum -= arr[(i-(m/2)-1)]if( (i+m/2) < n)
           sum += arr[(i+m/2)]sum_array[i] = sumprint sum_array

Implementation:

// CPP Program to find sum array for a given
// array.
#include <bits/stdc++.h>
using namespace std;

// function to calc sum_array and print
void calcSum_array(int arr[], int n, int m)
{
    int sum = 0;
    int sum_array[n];

    // calc 1st m/2 + 1 element for 1st window
    for (int i = 0; i < m / 2 + 1; i++)
        sum += arr[i];
    sum_array[0] = sum;

    // use sliding window to
    // calculate rest of sum_array
    for (int i = 1; i < n; i++) {
        if (i - (m / 2) - 1 >= 0)
            sum -= arr[i - (m / 2) - 1];
        if (i + (m / 2) < n)
            sum += arr[i + (m / 2)];
        sum_array[i] = sum;
    }

    // print sum_array
    for (int i = 0; i < n; i++)
        cout << sum_array[i] << " ";
}

// driver program
int main()
{
    int arr[] = { 3, 6, 2, 7, 3, 8, 4, 
                      9, 1, 5, 0, 4 };
    int m = 5;
    int n = sizeof(arr) / sizeof(int);
    calcSum_array(arr, n, m);
    return 0;
}

// Java Program to find sum array 
// for a given array.
class GFG 
{
    // function to calc sum_array and print
    static void calcSum_array(int arr[], int n, int m)
    {
        int sum = 0;
        int sum_array[] = new int[n];
    
        // calc 1st m/2 + 1 element
        // for 1st window
        for (int i = 0; i < m / 2 + 1; i++)
            sum += arr[i];
        sum_array[0] = sum;
    
        // use sliding window to
        // calculate rest of sum_array
        for (int i = 1; i < n; i++) 
        {
            if (i - (m / 2) - 1 >= 0)
                sum -= arr[i - (m / 2) - 1];
            if (i + (m / 2) < n)
                sum += arr[i + (m / 2)];
            sum_array[i] = sum;
        }
    
        // print sum_array
        for (int i = 0; i < n; i++)
            System.out.print(sum_array[i] + " ");
    }
    
    // Driver program
    public static void main(String[] args)
    {
        int arr[] = { 3, 6, 2, 7, 3, 8, 4, 9, 1, 5, 0, 4 };
        int m = 5;
        int n = arr.length;
        calcSum_array(arr, n, m);
    }
}

// This code is contributed by prerna saini.

# Python3 Program to find Sum array 
# for a given array.
import math as mt

# function to calc Sum_array and print
def calcSum_array(arr, n, m):

    Sum = 0
    Sum_array = [0 for i in range(n)]

    # calc 1st m/2 + 1 element for 1st window
    for i in range(m // 2 + 1):
        Sum += arr[i]
    Sum_array[0] = Sum

    # use sliding window to
    # calculate rest of Sum_array
    for i in range(1, n):
        if (i - (m // 2) - 1 >= 0):
            Sum -= arr[i - (m // 2) - 1]
        if (i + (m / 2) < n):
            Sum += arr[i + (m //2)]
        Sum_array[i] = Sum
    
    # print Sum_array
    for i in range(n):
        print(Sum_array[i], end = " ")

# Driver Code
arr = [ 3, 6, 2, 7, 3, 8, 4, 9, 1, 5, 0, 4 ]
m = 5
n = len(arr)
calcSum_array(arr, n, m)

# This code is contributed by mohit kumar 29

// C# Program to find sum array 
// for a given array.
using System;

class GFG 
{
    // function to calc sum_array and print
    static void calcSum_array(int []arr, int n, int m)
    {
        int sum = 0;
        int []sum_array = new int[n];
    
        // calc 1st m/2 + 1 element
        // for 1st window
        for (int i = 0; i < m / 2 + 1; i++)
            sum += arr[i];
        sum_array[0] = sum;
    
        // use sliding window to
        // calculate rest of sum_array
        for (int i = 1; i < n; i++) 
        {
            if (i - (m / 2) - 1 >= 0)
                sum -= arr[i - (m / 2) - 1];
            if (i + (m / 2) < n)
                sum += arr[i + (m / 2)];
            sum_array[i] = sum;
        }
    
        // print sum_array
        for (int i = 0; i < n; i++)
        Console.Write(sum_array[i] + " ");
    }
    
    // Driver program
    public static void Main()
    {
        int []arr = { 3, 6, 2, 7, 3, 8, 4, 9, 1, 5, 0, 4 };
        int m = 5;
        int n = arr.Length;
        calcSum_array(arr, n, m);
    }
}

// This code is contributed by vt_m.

<?php
// PHP Program to find sum array 
// for a given array.

// function to calc sum_array and print
function calcSum_array(&$arr, $n, $m)
{
    $sum = 0;
    $sum_array = array();

    // calc 1st m/2 + 1 element
    // for 1st window
    for ($i = 0; 
         $i < (int)($m / 2) + 1; $i++)
        $sum = $sum + $arr[$i];
    $sum_array[0] = $sum;

    // use sliding window to
    // calculate rest of sum_array
    for ($i = 1; $i < $n; $i++) 
    {
        if ($i - (int)($m / 2) - 1 >= 0)
            $sum = $sum - $arr[$i - 
                    (int)($m / 2) - 1];
        if ($i + (int)($m / 2) < $n)
            $sum = $sum + $arr[$i + 
                    (int)($m / 2)];
        $sum_array[$i] = $sum;
    }

    // print sum_array
    for ($i = 0; $i < $n; $i++)
        echo $sum_array[$i] . " ";
}

// Driver Code
$arr = array(3, 6, 2, 7, 3, 8, 
             4, 9, 1, 5, 0, 4 );
$m = 5;
$n = sizeof($arr);
calcSum_array($arr, $n, $m);

// This code is contributed by Mukul Singh
?>

<script>
// JavaScript Program to find sum array for a given
// array.

// function to calc sum_array and print
function calcSum_array(arr, n, m)
{
    let sum = 0;
    let sum_array = new Array(n);

    // calc 1st m/2 + 1 element for 1st window
    for (let i = 0; i < Math.floor(m / 2) + 1; i++)
        sum += arr[i];
    sum_array[0] = sum;

    // use sliding window to
    // calculate rest of sum_array
    for (let i = 1; i < n; i++)
    {
        if (i - Math.floor(m / 2) - 1 >= 0)
            sum -= arr[i - Math.floor(m / 2) - 1];
        if (i + Math.floor(m / 2) < n)
            sum += arr[i + Math.floor(m / 2)];
        sum_array[i] = sum;
    }

    // print sum_array
    for (let i = 0; i < n; i++)
        document.write(sum_array[i] + " ");
}

// Driver program

    let arr = [ 3, 6, 2, 7, 3, 8, 4,
                    9, 1, 5, 0, 4 ];
    let m = 5;
    let n = arr.length;
    calcSum_array(arr, n, m);

// This code is contributed by Surbhi Tyagi.
</script>

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