What’s the Real Range of Tencent QQ Numbers and How Bitmap Handles Their Deduplication?

1. QQ Number Range

QQ numbers are stored as a 4‑byte unsigned integer (uint32), so their theoretical value range is [0, 2^32‑1] (0 to 4,294,967,295). In practice the backend enforces a lower bound of 10001, a legacy setting from early QQ versions. Numbers close to the lower bound tend to be older, more “prestigious” accounts.

The maximum 10‑digit value (4294967295) is about 4.3 billion, which explains why QQ numbers have never exceeded 11 digits.

2. What Happens When All QQ Numbers Are Used?

Because QQ’s active user base is far below 4.3 billion and Tencent imposes registration limits, the ID space will not be exhausted in the foreseeable future. Inactive accounts may be reclaimed, but the exact reclamation logic is not disclosed. If the space ever ran out, Tencent would need to redesign its ID system.

3. Bitmap’s Connection to QQ Numbers

Interview questions often use the QQ‑ID scenario to test knowledge of bitmap techniques for deduplication. A bitmap uses one bit per possible ID to indicate presence (1) or absence (0). With 512 MB of memory (4 GB ÷ 8), you can represent all 2^32 possible QQ numbers.

Example bitmap implementation in C++:

#include <iostream>
#include <set>
#include <cstring>
using namespace std;

#define N 20          // example range 0‑19
#define SHIFT 5
#define MASK 0x1f
unsigned int a[1 + N / 32] = {0};

// set bit i to 1
void setOne(int i) { a[i >> SHIFT] |= (1 << (i & MASK)); }
// set bit i to 0
void setZero(int i) { a[i >> SHIFT] &= ~(1 << (i & MASK)); }
// get state of bit i
int getState(int i) { return (a[i >> SHIFT] & (1 << (i & MASK))) ? 1 : 0; }

int main() {
    setOne(1); setOne(3); setOne(4); setOne(9);
    for (int i = 0; i < N; ++i) {
        cout << i << " state: " << getState(i) << endl;
    }
    return 0;
}

Running the program prints the presence (1) or absence (0) of each number in the example range, demonstrating how a bitmap can both mark and deduplicate IDs.

Thus, understanding the QQ ID range and bitmap representation provides a practical illustration of how large‑scale identifier systems can be managed efficiently.