Added binary permutation generating code

Author: fredbr

math/a.out

@@ -0,0 +1,22 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+// generates next integer w with popcount(w) == popcount(v)
+uint32_t next_perm(uint32_t v) {
+    uint32_t t = (v | ( v - 1)) + 1;
+    uint32_t w = t | ((((t & -t) / (v & -v)) >> 1) - 1);
+    return w;
+}
+
+int main() {
+    int n;
+    cin >> n;
+        
+    // loop throught all the permutations with 1, 2, 3... bits set
+    for (int i = 1; i < n; i++) {
+        for (int x = (1<<i)-1; x < (1<<n); x = next_perm(x)) {
+            cout << bitset<8>(x) << "\n";
+        }
+    }
+}

math/binary_perm.cpp

@@ -0,0 +1,57 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+using ll = long long;
+
+[[ gnu::target("abm,bmi,bmi2") ]]
+inline int ilog2(ll x) {
+    return x==0? 0: 63 - __builtin_clzll(x);
+}
+
+inline ll isqrt(ll x) {
+    ll res = sqrtl(x);
+    while (res*res < x) res++;
+    return res;
+}
+
+inline ll mul(ll a, ll b, ll m) {
+    return __int128(a)*b%m;
+
+    // ll res = 0;
+    // while (b) {
+    //     if (b&1) b = (a+b)%m;
+    //     b = (b+b)%2;
+    //     b >>= 1;
+    // }
+    // return res;
+}
+
+ll phi(ll x) {
+    ll res = x;
+    
+    while (x % 2 == 0) {
+        res -= res/2;
+        x /= 2;
+    }
+
+    for (ll i = 3; i*i <= x; i += 2) {
+        while (x % i == 0) {
+            res -= res/i;
+            x /= i;
+        }
+    }
+
+    return res;
+}
+
+ll power(ll a, ll b, ll m) {
+    ll res = 1;
+    while (b) {
+        if (b&1) res = mul(res, a, m);
+        a = mul(a, a, m);
+        b >>= 1;
+    }
+    return res;
+}
+