Prefix Sum Array in DSA C - Build from Scratch

Prefix Sum Array

📖 Scenario: Imagine you have a list of daily sales numbers for a small shop. You want to quickly find the total sales from the start up to any given day.

🎯 Goal: You will build a prefix sum array that stores the running total of sales up to each day. This helps answer total sales queries efficiently.

📋 What You'll Learn

Create an integer array called sales with exactly these values: 5, 3, 8, 6, 2

Create an integer array called prefix_sum with the same length as sales

Create an integer variable called n and set it to the length of sales

Use a for loop with variable i from 0 to n - 1 to fill prefix_sum

Print the prefix_sum array elements separated by spaces

💡 Why This Matters

🌍 Real World

Prefix sums are used in finance to quickly calculate cumulative totals like sales or expenses over time.

💼 Career

Understanding prefix sums helps in data analysis, algorithm optimization, and solving range query problems efficiently.

1

Create the sales data array

Create an integer array called sales with exactly these values: 5, 3, 8, 6, 2.

DSA C

# Your code here

Hint

Use curly braces to list the values inside the array.

2

Create prefix sum array and length variable

Create an integer array called prefix_sum with length 5 and an integer variable called n set to 5.

DSA C

int sales[5] = {5, 3, 8, 6, 2};
# Your code here

Hint

Declare prefix_sum as an integer array of size 5 and n as an integer with value 5.

3

Fill the prefix sum array

Use a for loop with variable i from 0 to n - 1 to fill prefix_sum so that each element is the sum of all sales elements up to index i. For i == 0, set prefix_sum[0] to sales[0]. For other i, set prefix_sum[i] to prefix_sum[i - 1] + sales[i].

DSA C

int sales[5] = {5, 3, 8, 6, 2};
int prefix_sum[5];
int n = 5;

# Your code here

Hint

Use an if inside the loop to handle the first element separately.

4

Print the prefix sum array

Use a for loop with variable i from 0 to n - 1 to print each element of prefix_sum followed by a space. Then print a newline character.

DSA C

int sales[5] = {5, 3, 8, 6, 2};
int prefix_sum[5];
int n = 5;

for (int i = 0; i < n; i++) {
    if (i == 0) {
        prefix_sum[i] = sales[i];
    } else {
        prefix_sum[i] = prefix_sum[i - 1] + sales[i];
    }
}

# Your code here

Hint

Use printf("%d ", prefix_sum[i]) inside the loop and printf("\n") after the loop.