From 52bc203f6aa95341d718d0f8b8c52d4bf5b4e5da Mon Sep 17 00:00:00 2001
From: subcrip <contact@subc.rip>
Date: Wed, 29 May 2024 19:46:37 +0800
Subject: [PATCH] Add number/factcount.cc

Signed-off-by: subcrip <contact@subc.rip>
---
 number/factcount.cc | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 number/factcount.cc

diff --git a/number/factcount.cc b/number/factcount.cc
new file mode 100644
index 0000000..7bcb69c
--- /dev/null
+++ b/number/factcount.cc
@@ -0,0 +1,25 @@
+pair<vector<int>, vector<int>> factcount(int n) {
+    vector<bool> not_prime(n + 1);
+    vector<int> res(n + 1), num(n + 1);
+    vector<int> primes;
+    res[1] = 1;
+    for (int i = 2; i <= n; ++i) {
+        if (not not_prime[i]) {
+            res[i] = 2;
+            num[i] = 1;
+            primes.emplace_back(i);
+        }
+        for (auto&& x : primes) {
+            if (i * x > n) break;
+            not_prime[i * x] = 1;
+            if (i % x == 0) {
+                num[i * x] = num[i] + 1;
+                res[i * x] = res[i] / num[i * x] * (num[i * x] + 1);
+                break;
+            }
+            num[i * x] = 1;
+            res[i * x] = res[i] * 2;
+        }
+    }
+    return {primes, res};
+}