Reducing Integer Fractions Algorithm - Solution Explanation?
- by Andrew Tomazos - Fathomling
This is a followup to this problem:
Reducing Integer Fractions Algorithm
Following is a solution to the problem from a grandmaster:
#include <cstdio>
#include <algorithm>
#include <functional>
using namespace std;
const int MAXN = 100100;
const int MAXP = 10001000;
int p[MAXP];
void init() {
for (int i = 2; i < MAXP; ++i) {
if (p[i] == 0) {
for (int j = i; j < MAXP; j += i) {
p[j] = i;
}
}
}
}
void f(int n, vector<int>& a, vector<int>& x) {
a.resize(n);
vector<int>(MAXP, 0).swap(x);
for (int i = 0; i < n; ++i) {
scanf("%d", &a[i]);
for (int j = a[i]; j > 1; j /= p[j]) {
++x[p[j]];
}
}
}
void g(const vector<int>& v, vector<int> w) {
for (int i: v) {
for (int j = i; j > 1; j /= p[j]) {
if (w[p[j]] > 0) {
--w[p[j]];
i /= p[j];
}
}
printf("%d ", i);
}
puts("");
}
int main() {
int n, m;
vector<int> a, b, x, y, z;
init();
scanf("%d%d", &n, &m);
f(n, a, x);
f(m, b, y);
printf("%d %d\n", n, m);
transform(x.begin(), x.end(), y.begin(),
insert_iterator<vector<int> >(z, z.end()),
[](int a, int b) { return min(a, b); });
g(a, z);
g(b, z);
return 0;
}
It isn't clear to me how it works. Can anyone explain it?
The equivilance is as follows:
a is the numerator vector of length n
b is the denominator vector of length m
