How to find Minimum Maximum sum c++

Question

I've written some code in c++ that is meant to find the minimum and maximum values that can be calculated by summing 4 of the 5 integers presented in an array. My thinking was that I could add up all elements of the array and loop through subtracting each of the elements to figure out which subtraction would lead to the smallest and largest totals. I know this isn't the smartest way to do it, but I'm just curious why this brute force method isn't working when I code it. Any feedback would be very much appreciated.

#include <iostream>
#include <vector>
#include <limits.h>
using namespace std;

void minimaxsum(vector<int> arr){
    int i,j,temp;
    int n=sizeof(arr);
    int sum=0;
    int low=INT_MAX;
    int high=0;

    for (j=0;j<n;j++){
        for (i=0;i<n;i++){
            sum+=arr[i];
        }
        temp=sum-arr[j];
        if(temp<low){
            low=temp;
        }
        else if(temp>high){
            high=temp;
        }
    }
    cout<<low;
    cout<<high<<endl;
}

int main (){
    vector<int> arr;
    arr.push_back(1.0);
    arr.push_back(2.0);
    arr.push_back(3.0);
    arr.push_back(1.0);
    arr.push_back(2.0);
    minimaxsum(arr);
    return 0;
}

Answer 1

There are 2 problems.

1. Your code is unfortunately buggy and cannot deliver the correct result.
2. The solution approach, the design is wrong

I will show you what is wrong and how it could be refactored.

But first and most important: Before you start coding, you need to think. At least 1 day. After that, take a piece of paper and sketch your solution idea. Refactor this idea several times, which will take a complete additional day.

Then, start to write your code. This will take 3 minutes and if you do it with high quality, then it takes 10 minutes.

Let us look first at you code. I will add comments in the source code to indicate some of the problems. Please see:

#include <iostream>
#include <vector>
#include <limits.h>   // Do not use .h include files from C-language. Use limits
using namespace std;  // Never open the complete std-namepsace. Use fully qualified names

void minimaxsum(vector<int> arr) {  // Pass per reference and not per value to avoid copies
    int i, j, temp;                 // Always define variables when you need them, not before. Always initialize
    int n = sizeof(arr);            // This will not work. You mean "arr.size();"
    int sum = 0;
    int low = INT_MAX;              // Use numeric_limits from C++
    int high = 0;                   // Initialize with MIN value. Otherwise it will fail for negative integers

    for (j = 0; j < n; j++) {       // It is not understandable, why you use a nested loop, using the same parameters
        for (i = 0; i < n; i++) {   // Outside sum should be calculated only once 
            sum += arr[i];          // You will sum up always. Sum is never reset
        }
        temp = sum - arr[j];
        if (temp < low) {
            low = temp;
        }
        else if (temp > high) {
            high = temp;
        }
    }
    cout << low;                    // You miss a '\n' at the end
    cout << high << endl;           // endl is not necessary for cout. '\n' is sufficent
}

int main() {
    vector<int> arr;               // use an initializer list
    arr.push_back(1.0);            // Do not push back doubles into an integer vector
    arr.push_back(2.0);
    arr.push_back(3.0);
    arr.push_back(1.0);
    arr.push_back(2.0);
    minimaxsum(arr);
    return 0;
}

Basically your idea to subtract only one value from the overall sum is correct. But there is not need to calculate the overall sum all the time.

Refactoring your code to a working, but still not an optimal C++ solution could look like:

#include <iostream>
#include <vector>
#include <limits>

// Function to show the min and max sum from 4 out of 5 values
void minimaxsum(std::vector<int>& arr) {

    // Initialize the resulting values in a way, the the first comparison will always be true
    int low = std::numeric_limits<int>::max();
    int high = std::numeric_limits<int>::min();;              

    // Calculate the sum of all 5 values
    int sumOf5 = 0;
    for (const int i : arr)
        sumOf5 += i;
    
    // Now subtract one value from the sum of 5
    for (const int i : arr) {
        if (sumOf5 - i < low)       // Check for new min
            low = sumOf5 - i;
        if (sumOf5 - i > high)      // Check for new max
            high = sumOf5 - i;      
    }
    std::cout << "Min: " << low << "\tMax: " << high << '\n';
}

int main() {
    std::vector<int> arr{ 1,2,3,1,2 };   // The test Data
    minimaxsum(arr);                     // Show min and max result
}