removing the erase hotspot from the vector

labs/counting/main.cpp

@@ -25,6 +25,8 @@ std::vector<int> readNumbers(const char* filename) {
 
 	// read the numbers in (first line = number of inputs)
 	std::fscanf( fp, "%d", &nCount);
+    numbers.reserve(nCount);
+
 	for (int i=0; i<nCount; ++i) {
 		int nextNum = 0;
 		std::fscanf( fp, "%d", &nextNum);
@@ -40,13 +42,13 @@ std::vector<int> readNumbers(const char* filename) {
  * @param numbers the numbers to calculate
  * @return the average of the input values
  */
-float calcAverage(std::vector<int> numbers) {
+float calcAverage(std::vector<int>& numbers) {
 	int total = 0;
 	int size = 0;
 
 	while ( !numbers.empty() ) {
-		total += numbers[0];
-		numbers.erase( numbers.begin() );
+		total += numbers.back();
+        numbers.pop_back();
 		size++;
 	}
 
@@ -84,7 +86,7 @@ int main(int argc, const char* argv[]) {
 	}
 
 	// calculate and print the average
-	auto avg = calcAverageFast(numbers);
+	auto avg = calcAverage(numbers);
 	std::cout << "the average is: " << avg << std::endl;
 
 	return EXIT_SUCCESS;