add codeforces solutions folder

leetcode/lc762.cpp

@@ -0,0 +1,30 @@
+class Solution{
+    public:
+        int countPrimeSetBits(int left, int right){
+            int ans = 0;
+            for(int i = left;i<=right;i++){
+                if(isPrime(__builtin_popcount(i)))
+                    ans++;
+            }
+            return ans;
+        }
+        bool isPrime(int n){
+            if(n<2) return false;
+            for(int i =2;i*i<=n;i++)
+                if(n%i == 0) return false;
+            return true;
+        }
+};
+//TC : o(right-left+1)
+//SC : o(1)
+
+/*
+int countPrimeSetBits(int L, int R) {
+        int cnt = 0, hash[20] = {0, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1};
+        for (int i = L; i <= R; i++) {
+            bitset<20> b(i);
+            if(hash[b.count()]) cnt++;
+        }
+        return cnt;
+    }
+    */