Find the second largest number in a vector

Description: Find the second largest number in {12, 35, 1, 10, 34, 1} without sorting.

Hint:

• Keep largest and second, and update both in one loop.

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Solution

#include <climits>
#include <iostream>
#include <vector>

int second_largest(const std::vector<int>& v) {
    int largest = INT_MIN, second = INT_MIN;
    for (int n : v) {
        if (n > largest) {
            second = largest;
            largest = n;
        } else if (n > second && n != largest) {
            second = n;
        }
    }
    return second;
}

int main() {
    std::cout << second_largest({12, 35, 1, 10, 34, 1}) << '\n';
    std::cout << second_largest({5, 5, 5, 2}) << '\n';
}

How it works

• When a bigger value comes, the old biggest becomes the second one.

Read C++ Vectors.

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