Java program to find running sum of array

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  • Given one dimensional array in java.
  • Calculate running sum of array.

Example to find running sum of array

Example 1:
 
Input: nums = [1,2,3,4]
Output: [1,3,6,10]
Explanation: Running sum is obtained as follows: [1, 1+2, 1+2+3, 1+2+3+4].
 
Example 2:
 
Input: nums = [1,1,1,1,1]
Output: [1,2,3,4,5]
Explanation: Running sum is obtained as follows: [1, 1+1, 1+1+1, 1+1+1+1, 1+1+1+1+1].
 
 
Example 3:
 
Input: nums = [3,1,2,10,1]
Output: [3,4,6,16,17]

Algorithm to calculate running sum of array:

Calculate sum by modify original array:

  • Loop through original array.
  • Calculate sum of current element and sum of previous elements.
  • Return original array

Calculate sum without modifying original array:

  • Create new array equal to length of original array.
    • int[] output = new int[nums.length]
  • Copy first element from original array to new array.
    • output[0]=nums[0];
  • Loop through original array.
    • Add current element of original array & sum of previous elements.
    • output[iElement] = nums[iElement] + output[iElement-1] ;
  • Return output array

Program to calculate running sum of array in java

package org.learn;
 
import java.util.Arrays;
 
public class RunningSumOfArray {
 
    public static int[] runningSumCreateCopy(int[] nums) {
 
        int[] output = new int[nums.length];
 
        output[0] = nums[0];
        for (int iElement = 1; iElement < nums.length; iElement++) {
            output[iElement] = output[iElement - 1] + nums[iElement];
        }
        return output;
    }
 
    public static int[] runningSum(int[] nums) {
 
        for (int iElement = 1; iElement < nums.length; iElement++) {
            nums[iElement] += nums[iElement - 1];
        }
        return nums;
    }
 
    public static void main(String[] args) {
 
        int[] nums = {1,2,3,4};
        System.out.println("Input Array : "+Arrays.toString(nums));
 
        System.out.println("Output Array:");
        System.out.println(Arrays.toString(runningSumCreateCopy(nums)));
        System.out.println(Arrays.toString(runningSum(nums)));
 
        int[] arr = {1,1,1,1,1};
        System.out.println("\nInput Array : "+Arrays.toString(arr));
 
        System.out.println("Output Array:");
        System.out.println(Arrays.toString(runningSumCreateCopy(arr)));
        System.out.println(Arrays.toString(runningSum(arr)));
 
    }
}

Output: calculate running sum of array in java

Input Array : [1, 2, 3, 4]
Output Array:
[1, 3, 6, 10]
[1, 3, 6, 10]
 
Input Array : [1, 1, 1, 1, 1]
Output Array:
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

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