DATA STRUCTURES PROGRAM • ARRAY TECHNIQUES

Find a Missing Number Using XOR

Learn how to find a missing number using xor using a clear C program.

BeginnerXORCancellationMissing value

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

Missing number = 2

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int values[] = {3, 0, 1};
    int missing = 3;
    for (int index = 0; index < 3; index++) missing ^= index ^ values[index];
    printf("Missing number = %d\n", missing);
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Missing number = 2

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
XOR all expected indices with all stored values so equal numbers cancel.
Display the computed result.

XOR all expected indices with all stored values so equal numbers cancel.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(1)

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.