code-sum.cpp

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 * Code for the book "DAILY 43: Algorithmic Problems for Coding Interviews: Easy level, C++ edition"
 *
 * Licensed under the GNU General Public License, Version 3.0 (the "License");
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#include <iostream>
#include <vector>

int missingNumber(std::vector<int>& nums) {
    int index = 0, size = nums.size();
    // N will be missed in the loop
    int missing = size;
    // expected_sum = size * (size+1) / 2;
    // Not computing directly to avoid overflow
    for (; index < size; ++index) {
        // sum = sum + nums[index]
        // expected = expected + index
        // missing = expected - sum
        missing = missing + (index - nums[index]);
    }
    return missing;
}

int main() {
    std::vector<int> nums = {3, 0, 1}; // Example input
    std::cout << "Missing number: " << missingNumber(nums) << std::endl;

    std::vector<int> nums2 = {9,6,4,2,3,5,7,0,1}; // Another example input
    std::cout << "Missing number: " << missingNumber(nums2) << std::endl;

    return 0;
}