Merge pull request #495 from Naman2251/main

day8sol2

Author: Dheeraj-06

Problems/Mathematics/Day-08/sol/Naman2251/Solution2.cpp

@@ -0,0 +1,57 @@
+//Submission Link: https://codeforces.com/contest/1999/submission/356264212
+
+/*
+First I counted the number of one and zeros then I calculated the permutation possible for getting k element using one or zero. THen by
+applying pnc calculated the number of subsequences.
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+#define fastio ios::sync_with_stdio(false); cin.tie(NULL);
+ 
+const long long mod=1e9+7;
+ 
+vector<long long> fact(200001);
+ 
+long long binexp(long long a, long long b) {
+    long long ans = 1;
+    a %= mod;
+    while (b) {
+        if (b & 1) ans = ans * a % mod;
+        a = a * a % mod;
+        b >>= 1;
+    }
+    return ans%mod;
+}
+ 
+long long C(long long n, long long r) {
+    if (r < 0 || r > n) return 0;
+    long long ans=fact[n] * binexp(fact[r], mod - 2) % mod;
+    ans*=binexp(fact[n - r], mod - 2) % mod;
+    return ans%mod;
+}
+
+int main() {
+    fastio;
+    fact[0]=1;
+    for(long long i=1; i<200001; i++) fact[i]=(fact[i-1]*i)%mod;
+    long long t;
+    cin>>t;
+    while(t--) {
+        long long n, k;
+        cin>>n>>k;
+        vector<int> a(n), cnt(2,0);
+        for(int i=0; i<n; i++) {
+            cin>>a[i];
+            cnt[a[i]]++;
+        }
+        long long ans=0;
+        for(long long i=0; i<=cnt[0]; i++) {
+            int b=k-i;
+            if(b>=0 && b<=cnt[1]) {
+                if(b>i) ans+=(C(cnt[0], i)%mod)*(C(cnt[1], b)%mod)%mod;
+            }
+        }
+        cout<<ans%mod<<endl;
+    }
+}