这是我针对半素数计数问题的解决方案,该解决方案对于小型和中型输入是正确的,但会导致大型测试用例的段错误。
https://codility.com/demo/results/demo8JU794-FC7/
这通常发生在无效指针等情况下。但是我在这里看不到任何可能导致这种行为的内容。
你能发现代码有什么问题吗?
vector<int> solution(int N, vector<int> &P, vector<int> &Q) {
int M = P.size();
// Use sieve of eratosthenes to find prime numbers within range 0 to N
vector<int> sieve(N+1);
sieve[0] = sieve[1] = 0;
for (int i = 2; i <= N; ++i)
{
if (sieve[i] == 0)
{
int k = i * i;
while(k <= N)
{
// For each non prime store its lowest prime divisor.
sieve[k] = i;
k += i;
}
}
}
vector<int> answer(M);
for (int i = 0; i < M; ++i)
{
// Count semiprimes for each range (P[i], Q[i])
int count = 0;
for(int j = P[i]; j <= Q[i]; ++j)
{
// If a number is divisible by prime and the result of this division is also a prime
// Then it's a semiprime.
if (sieve[j] != 0 && sieve[j / sieve[j]] == 0)
{
count++;
}
}
answer[i] = count;
}
return answer;
}
最佳答案
在这一部分中,对于 N = 50000,k = i * i
的结果溢出了一个 int,这就是段错误的原因。
if (sieve[i] == 0)
{
int k = i * i;
while(k <= N)
{
// For each non prime store its lowest prime divisor.
sieve[k] = i;
k += i;
}
}
关于c++ - Codility代码导致段错误,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21946344/