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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3.  
  4. /* Allocate 1MB in memory pool and use this memory only to assign whenever somebody ask for memory */
  5. template <typename T>
  6. struct Allocator {
  7.     using value_type = T; // type alias
  8.     unordered_map<size_t, size_t> memHash;
  9.  
  10.     Allocator() {
  11.         int one_mb = 1024 * 1024;
  12.         void * add = malloc(one_mb);
  13.         memHash[(size_t)add] = one_mb;
  14.     }
  15.  
  16.     // n is number of items
  17.     T* allocate(size_t n) {
  18.         n *= sizeof(T);
  19.         for (auto &[address, sz]: memHash) {
  20.             if (sz < n) continue;
  21.             if (sz > n) {
  22.                 memHash[address + n] = sz - n; // [0, 10], [13, 19]
  23.             }
  24.             memHash.erase(address);
  25.             return (T *)address;
  26.         }
  27.         return nullptr;
  28.         // return (T *)malloc(n * sizeof(T)); // n bytes
  29.     }
  30.  
  31.     void deallocate(T *ptr, size_t sz) {
  32.         memHash[(size_t)ptr] = sz;
  33.         if (memHash.count((size_t)ptr + sz)) {
  34.             memHash[(size_t)ptr] = sz + memHash[(size_t)ptr + sz];
  35.             memHash.erase((size_t)ptr + sz);
  36.         }
  37.         // free(ptr);
  38.     }
  39. };
  40.  
  41. int main()
  42. {
  43.     vector<int, Allocator<int>> v;
  44.     for (int i = 0; i < 10; i++) v.emplace_back(i);
  45.     for (auto &i: v) cout << i << " ";
  46.     cout << "\n";
  47.  
  48.     return 0;
  49. }
Success #stdin #stdout 0s 5300KB
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https://ideone.com/7TnACr
language:
C++ (gcc 8.3)
created:
4 days ago
visibility:
public

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