vector<vector<int> > fourSum(vector<int> &num, int target) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (num.size() < 4)
return result;
//O(n ^ 2)
v.clear();
result.clear();
for (size_t i = 0; i < num.size(); ++i)
{
for (size_t j = i + 1; j < num.size(); ++j)
{
TwoSum t;
t.value = num[i] + num[j];
t.pos1 = i;
t.pos2 = j;
v.push_back(t);
}
}
//O(n ^ 2 log (n ^ 2))
sort(v.begin(), v.end(), my_compare);
//O(n)
cut_the_tail(target);
for (size_t i = 0; i < v.size(); ++i)
{
//O(log (n ^ 2))
size_t begin = my_binary_search_begin(target - v[i].value, i + 1, v.size() - 1); //reduce the running time
size_t end = my_binary_search_end(target - v[i].value, i + 1, v.size() - 1); //reduce the running time
//O(n ^ 2)
for (size_t j = begin; j <= end; ++j)
{
if (v[i].pos1 == v[j].pos1 || v[i].pos2 == v[j].pos1
|| v[i].pos1 == v[j].pos2 || v[i].pos2 == v[j].pos2) //v[m] and v[n] share a same element
continue;
else
{
vector<int> temp;
temp.push_back(num[v[i].pos1]);
temp.push_back(num[v[i].pos2]);
temp.push_back(num[v[j].pos1]);
temp.push_back(num[v[j].pos2]);
sort(temp.begin(), temp.end());
if (find(result.begin(), result.end(), temp) == result.end())
result.push_back(temp);
}
}
}
return result;
}
static void RandInts(
vec_int& ints, // out: scrambled integers in range 0 ... NSIZE(ints)-1
int seed) // in: random seed
{
const int n = NSIZE(ints);
CV_Assert(n > 0);
if (n > RAND_MAX)
Err("vector size %d is too big (max allowed is %d)", n, RAND_MAX);
CV_Assert(seed != 0);
if (seed == 1) // 1 has a special meaning which we don't want
seed = int(1e6); // arb
int i;
for (i = 0; i < n; i++)
ints[i] = i;
srand(seed);
// We use our own random shuffle here because different compilers
// give different results which messes up regression testing.
// (I think only Visual C 6.0 is incompatible with everyone else?)
//
// Following code is equivalent to
// random_shuffle(ints.begin(), ints.end(),
// pointer_to_unary_function<int,int>(RandInt));
vec_int::iterator it = ints.begin();
for (i = 2; ++it != ints.end(); i++)
iter_swap(it, ints.begin() + rand() % n);
}
void monomial_mul(const vec_int &A, const vec_int &B, vec_int &C)
{
auto a = A.begin();
auto b = B.begin();
auto c = C.begin();
for (; a != A.end(); ++a, ++b, ++c) {
*c = *a + *b;
}
}