The second problem on the spoj:"Prime Generator"

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C++

generator

Hello,when I try to solve the second problem about Prime Generator on the http://www.spoj.com/[^] in C++(4.0.0-8),it runs to me a trouble that I can compile and run well on my own computer,but when I sent it to spoj, the result is "wrong answer ".
The problem is:

Input : The input begins with the number t of test cases in a single line (t<=10). In each of the next t lines there are two numbers m and n (1 <= m <= n <= 1000000000, n-m<=100000) separated by a space.

Output : For every test case print all prime numbers p such that m <= p <= n, one number per line, test cases separated by an empty line.

Example

Input:
2
1 10
3 5

Output:
2
3
5
7

3
5

My answer is:

#include <iostream>
#include <sstream>
#include <map>
#include <list>
#include <math.h>

using namespace std;

bool isPrime(int num)
{
    if(num <= 2)
        return num == 2;
    else if(num % 2 == 0)
        return false;
    else
    {
        int Sqrt = sqrt(num);
        for(int i = 3;i<=Sqrt;i+2)
        {
            if(num%i == 0)
                return false;
            else
                return true;
        }
    }
    return true;
}

list<int> getPrime(int m,int n)
{
    list<int> li;
    if(1 <= m && m <= n && n <= 1000000000 && n-m<=100000)
    {
        if(n >= 2)
        {
            for(int k = m;k<=n;k++)
            {
                if(isPrime(k))
                {
                    li.push_back(k);
                }
            }
        }
    }
    return li;
}


int main()
{
    stringstream ss;
    int t = 0;
    cin >> t;
    map<int,int> nMap;
    int a,b;
    if(t >= 0 && t <= 10)
    { 
        while(t-- > 0)
        {
            cin >> a >> b;
            nMap.insert(pair<int,int>(a,b));
        }
    }
    map<int,int>::iterator mi;
    int oi = 0;
    for(mi = nMap.begin();mi != nMap.end();mi++)
    {
        list<int> ll = getPrime(mi->first,mi->second);
        list<int>::iterator lit;
        for(lit = ll.begin();lit !=ll.end();lit++)
        {
            cout << *lit << endl;
        }
        cout << endl;
    }
}

What's the problem in my codes,how can I fix it,please help me,thank you!
I'm very appreciate if you can tell me how to optimaze my code's performance~