Create 56_codechef_Chef_and_Interesting_Subsequences.cpp

Author: Prince-1501

56_codechef_Chef_and_Interesting_Subsequences.cpp

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+//
+//  main.cpp
+//  code
+//
+//  Created by Prince  Kumar on 23/09/19.
+//  Copyright © 2019 Prince  Kumar. All rights reserved.
+//
+//  code of Chef and Interesting Subsequences
+//  ** --- September long challenge  -- ** //
+
+#include <iostream>
+#include <vector>
+#include <algorithm>
+#define ll long long
+using namespace std;
+ll int gcd(ll int a, ll int b)
+{
+    if(b==0)
+        return a;
+    else
+        return gcd(b,a%b);
+}
+void nCr(int n, int r)
+{
+    
+    // p holds the value of n*(n-1)*(n-2)...,
+    // k holds the value of r*(r-1)...
+    long long p = 1, k = 1;
+    
+    // C(n, r) == C(n, n-r),
+    // choosing the smaller value
+    if (n - r < r)
+        r = n - r;
+    
+    if (r != 0) {
+        while (r) {
+            p *= n;
+            k *= r;
+            
+            // gcd of p, k
+            long long m = gcd(p, k);
+            
+            // dividing by gcd, to simplify product
+            // division by their gcd saves from the overflow
+            p /= m;
+            k /= m;
+            
+            n--;
+            r--;
+        }
+        
+        // k should be simplified to 1
+        // as C(n, r) is a natural number
+        // (denominator should be 1 ) .
+    }
+    
+    else
+        p = 1;
+    
+    // if our approach is correct p = ans and k =1
+    cout << p << endl;
+}
+int main()
+{
+    int T; cin>>T;
+    while(T--)
+    {
+        vector<int> v;
+        int n,k;cin>>n>>k;
+        for(int i=0;i<n;i++)
+        {
+            int x; cin>>x;
+            v.push_back(x);
+        }
+        sort(v.begin(),v.end());
+        int last_index_of_k = v[k-1];
+        int count=0;
+        for(int i=0;i<n;i++)
+        {
+            if(v[i]==last_index_of_k)
+                count++;
+        }
+        // we get total number of last_element
+        
+        int num=0;
+        for(int i=0;i<k;i++)
+        {
+            if(v[i]==last_index_of_k)
+                num++;
+        }
+        nCr(count,num);  // countCnum
+        
+    }
+}
+
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