Find the index of the minimum element in a subarray - c++

Question

The function FindSubArrayMinimum is suppose to return the index of the minimum value in an array between the values (left,right). Instead of returning 1 as it should, it returns 7.
Here is my code:
#include <iostream>
using namespace std;
class Minimum {
int *array;
int arrayLen;
public:
Minimum(int *array, int arrayLen) {
}
void swap(int &a, int &b) {
int x;
x = a;
a = b;
b = x;
}
int findMinimum(int a, int b) {
if(a < b){
return a;
}else{
return b;
}
}
int findArrayMinimum(int a[], int arraySize) {
int min=a[0];
for(int i=0;i<arraySize-1;i++){
if(a[i] < min){
min = i;
}
}
return min;
}
int findSubArrayMinimum(int a[], int arraySize, int left, int right) {
int min = a[left];
for(int i=left;i<right+1;i++){
if(a[i] < min){
cout << min << endl;
min = i;
}
}
return min;
}
int findSubArrayMinimumAndSwap(int left, int right, int swapIndex) {
}
};
int main() {
int A[5] = {47, 7, 21, -1, 11};
Minimum min(A, 5);
cout << "Minimum of 7 and 11 is " << min.findMinimum(7, 11) << endl;
int x = 5, y = 7;
min.swap(x, y);
cout << "x = " << x << ", y = " << y << endl;
cout << "Minimum value is at position " << min.findArrayMinimum(A,5) << endl;
cout << "Minimum value between [1,2] is at position " <<
min.findSubArrayMinimum(A,5,1,2)<< endl;
return 0;
}
I cannot for the life of me figure out why it won't return the minimum index. Logically speaking it should work unless I'm missing something?

Answer 1

all of my other functions as all the ones I have finished I have working.
It is not true. In findArrayMinimum the loop should be
for(int i=0;i<arraySize;i++)
Or
for(int i=0;i<=arraySize-1;i++)
The initial value an the condition in the loop are also wrong. Should be int min=0 and if(a[i] < a[min])
Instead of returning 1 as it should, it returns 7.
findSubArrayMinimum is nice, except initial minimum value int min = a[left], should be int min = left and the condition in the loop should be if(a[i] < a[min]).
arraySize is odd in findSubArrayMinimum, it is not used.
Your do not need the separate implementation for findSubArray. You can do return findSubArrayMinimum(a, 0, arraySize - 1) in findSubArray.
If you would implement the tests with arrays of 0, 1, many elements, with the left, right, middle subarrays, you would discover all bugs in your code.

Answer 2

C++ is all about not re-inventing wheels.
#include <algorithm>
size_t findArrayMinimum(int a[], size_t arraySize) {
// Returns index of minimum element
return std::min_element(a, a + arraySize) - a;
}

Answer 3

In your findSubArrayMinumum you need min = a[i]; and not min = i; i is a index and a[i] is value.
I suggested you:
int findSubArrayMinimum(int a[], int arraySize, int left, int right) {
int index = left;
int min = a[left];
for(int i=left;i<right+1;i++){
if(a[i] < min){
min = a[min];
index = i;
}
}
return index;
}
int index = min.findSubArrayMinimum(A,5,1,3);
cout << "Minimum value between [1,2] is at position " << index <<
". and value is: " << A[index] << endl;

Answer 4

int findSubArrayMinimum(int a[], int arraySize, int left, int right) {
//The min is the index of minimum value since you are returning the index only
int min = left;
for(int i=left;i<=right;i++){
//since we have min = indexOfMin, then we need to compare the values
if(a[i] <= a[min]){
min = i;
}
}
//remember! You are returning the index of the minmum value!
return min;
}