DATA STRUCTURES PROGRAM • ARRAY TECHNIQUES

Answer Range-Sum Queries with Prefix Sums

Learn how to answer range-sum queries with prefix sums using a clear C program.

BeginnerPrefix sumRange queryPreprocessing

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

Range sum [1,4] = 11

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int values[] = {3, 1, 4, 1, 5, 9};
    int prefix[7] = {0};
    for (int index = 0; index < 6; index++) prefix[index + 1] = prefix[index] + values[index];
    int left = 1, right = 4;
    printf("Range sum [%d,%d] = %d\n", left, right, prefix[right + 1] - prefix[left]);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Range sum [1,4] = 11

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Store cumulative sums so a range is the difference between two prefix positions.
Display the computed result.

Store cumulative sums so a range is the difference between two prefix positions.

EFFICIENCY

Time and space complexity

Time complexity

O(n) preprocessing, O(1) query

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.