Added construct the array in DP

README.md

@@ -25,6 +25,7 @@ easily understandable algorithms for learning purposes.
     * [Square Subsequences](hacker-rank/algorithms/dynamic-programming/square-subsequences)
     * [Stock Maximize](hacker-rank/algorithms/dynamic-programming/stock-maximize)
     * [Summing Pieces](hacker-rank/algorithms/dynamic-programming/summing-pieces)
+    * [Construct the Array](hacker-rank/algorithms/dynamic-programming/construct-the-array)
   - [Graph Theory](hacker-rank/algorithms/graph-theory)
     * [BFS: Shortest Reach](hacker-rank/algorithms/graph-theory/bfs-shortest-reach)
     * [Crab Graphs](hacker-rank/algorithms/graph-theory/crab-graphs)

hacker-rank/algorithms/dynamic-programming/construct-the-array/README.md

@@ -0,0 +1,3 @@
+# README
+
+[https://www.hackerrank.com/challenges/construct-the-array/problem](https://www.hackerrank.com/challenges/construct-the-array/problem)

hacker-rank/algorithms/dynamic-programming/construct-the-array/main.cpp

@@ -0,0 +1,52 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+typedef long long ll;
+#define mod 1000000007
+
+ll power(ll x, ll y) 
+{ 
+    ll res = 1;      // Initialize result 
+
+    x = x % mod;  // Update x if it is more than or  
+                // equal to p 
+
+    while (y > 0) 
+    { 
+        // If y is odd, multiply x with result 
+        if (y & 1) 
+            res = (res*x) % mod; 
+
+        // y must be even now 
+        y = y>>1; // y = y/2 
+        x = (x*x) % mod;   
+    } 
+    return res; 
+} 
+// Complete the countArray function below.
+ll countArray(ll n, ll k, ll x) {
+    // Return the number of ways to fill in the array.
+    if(n == 2){
+    if(x == 1)
+    return 0;
+    return 1;
+    }
+    ll a = power(k - 1, n - 2) - countArray(n - 1, k, x);
+    a = (a + mod) % mod;
+    return a;
+
+}
+
+int main()
+{
+
+    ll n,k,x;
+    cin >> n >> k >> x;
+
+    ll answer = countArray(n, k, x);
+
+    cout << answer << "\n";
+
+    return 0;
+}
+