Это именно то, что вам нужно (количество каждого числа в массиве):
// we'll store amounts of numbers like key-value pairs.
// std::map does exactly what we need. As a key we will
// store a number and as a key - corresponding counter
std::map<int, size_t> digit_count;
// it is simpler for explanation to have our
// array on stack, because it helps us not to
// think about some language-specific things
// like memory management and focus on the algorithm
const int arr[] = { 5, 2, 3, 2, 5 };
// iterate over each element in array
for(const auto elem : arr)
{
// operator[] of std::map creates default-initialized
// element at the first access. For size_t it is 0.
// So we can just add 1 at each appearance of the number
// in array to its counter.
digit_count[elem] += 1;
}
// Now just iterate over all elements in our container and
// print result. std::map's iterator is a pair, which first element
// is a key (our number in array) and second element is a value
// (corresponding counter)
for(const auto& elem : digit_count) {
std::cout << elem.first << " appeared " << elem.second << " times\n";
}
https://godbolt.org/z/_WTvAm
Хорошо, давайте напишем некоторые основы c код, но сначала давайте рассмотрим алгоритм (он не самый эффективный, но более понятный):
Самый понятный способ - перебирать каждое число в массиве и увеличивать некоторый соответствующий счетчик на единицу. Пусть это будет пара с первым элементом, который будет нашим номером, а вторым - счетчиком:
struct pair {
int number;
int counter;
};
Другая часть алгоритма будет объяснена в коде ниже
// Say that we know an array length and its elements
size_t length = // user-defined, typed by user, etc.
int* arr = new int[length];
// input elements
// There will be no more, than length different numbers
pair* counts = new pair[length];
// Initialize counters
// Each counte will be initialized to zero explicitly (but it is not obligatory,
// because in struct each field is initialized by it's default
// value implicitly)
for(size_t i = 0; i < length; i++) {
counts[i].counter = 0;
}
// Iterate over each element in array: arr[i]
for(size_t i = 0; i < length; i++)
{
// Now we need to find corresponding counter in our counters.
size_t index_of_counter = 0;
// Corresponding counter is the first counter with 0 value (in case when
// we meet current number for the first time) or the counter that have
// the corresponding value equal to arr[i]
for(; counts[index_of_counter].counter != 0 && counts[index_of_counter].number != arr[i]; index_of_counter++)
; // Do nothing here - index_of_counter is incrementing in loop-statement
// We found an index of our counter
// Let's assign the value (it will assign a value
// to newly initialized pair and won't change anything
// in case of already existing value).
counts[index_of_counter].number = arr[i];
// Increment our counter. It'll became 1 in case of new
// counter, because of zero assigned to it a bit above.
counts[index_of_counter].counter += 1;
}
// Now let's iterate over all counters until we reach the first
// containing zero (it means that this counter and all after it are not used)
for(size_t i = 0; i < length && counts[i].counter > 0; i++) {
std::cout << counts[i].number << " appeared " << counts[i].counter << " times\n";
}
// correctly delete dynamically allocated memory
delete[] counts;
delete[] arr;
https://godbolt.org/z/hN33Pn
Более того, это точно такое же решение, как и с std::map (та же идея), поэтому я надеюсь, что оно поможет вам понять, как работает первое решение внутри