STL Algorithms

STL Algorithms

The C++ Standard Library provides a rich set of algorithms in <algorithm> and <numeric> that operate on ranges (pairs of iterators). These algorithms replace hand-written loops with expressive, well-tested operations.

Sorting

std::sort sorts elements in ascending order by default:

#include <algorithm>
#include <vector>

vector<int> v = {5, 2, 8, 1, 9};
sort(v.begin(), v.end());
// v is now {1, 2, 5, 8, 9}

Searching

std::find returns an iterator to the first matching element:

auto it = find(v.begin(), v.end(), 8);
if (it != v.end()) {
    cout << "Found: " << *it << endl;
}

Counting

std::count counts how many elements match a value:

vector<int> nums = {1, 2, 3, 2, 4, 2};
int twos = count(nums.begin(), nums.end(), 2);
// twos == 3

Accumulate (Sum / Fold)

std::accumulate (from <numeric>) computes a running total:

#include <numeric>

vector<int> v = {1, 2, 3, 4, 5};
int total = accumulate(v.begin(), v.end(), 0);
// total == 15

Transform

std::transform applies a function to each element and stores the result:

vector<int> src = {1, 2, 3};
vector<int> dst(3);
transform(src.begin(), src.end(), dst.begin(),
    [](int x) { return x * x; });
// dst == {1, 4, 9}

Predicates: any_of / all_of

These test whether elements satisfy a condition:

vector<int> v = {2, 4, 6, 8};
bool allEven = all_of(v.begin(), v.end(),
    [](int x) { return x % 2 == 0; });
// allEven == true

bool anyNeg = any_of(v.begin(), v.end(),
    [](int x) { return x < 0; });
// anyNeg == false

Why Use STL Algorithms?

1. Correctness — battle-tested implementations
2. Readability — sort(v.begin(), v.end()) is clearer than a hand-rolled sort
3. Performance — optimized by compiler vendors
4. Composability — algorithms chain together naturally

Your Task

Implement simplified versions of common STL algorithms as standalone functions:

1. bubbleSort — sort a vector of integers in ascending order
2. findValue — return the index of a value (-1 if not found)
3. countValue — count occurrences of a value
4. accumulate — sum all elements starting from an initial value

Print the results as shown in the tests.