add codeforces solutions folder

leetcode/lc191.cpp

@@ -0,0 +1,18 @@
+class Solution{
+    public:
+        int hammingWeight(int n){
+            int res= 0;
+            /*for(int i = 0;i<32;i++){
+                if(n>>i && 1) res ++;
+            }*/
+            
+            //brian-kernighan's algo    
+            while(n){
+                n = n&(n-1);
+                res++
+
+            }
+            return res;
+        }
+};
+//n&n-1 resets the last set bit to 0, brian's algo takes o(number of set bits to run) unlike brute force which takes o(total no. of bits). both are o(1).