C++|| EASY || FULLY COMMENTED
```\n bool isValidSerialization(string pre) {\n       //vacancy will be counted for every node .. vacancy means the number of more nodes that current node can g
```\n bool isValidSerialization(string pre) {\n       //vacancy will be counted for every node .. vacancy means the number of more nodes that current node can generate i.e left and right child\n        \n        //initially root will occupy only 1 vacancy hence vacancy =1\n        int vac=1;\n        for(int i=0;i<pre.size();i++)\n        {\n            //if we encounter a , then do nothing\n            if(pre[i]==\',\')\n                continue;\n            \n            //reduce the vacancy as the current value eats up a vacancy by becoming the child of the previous parent node\n            vac--;\n            //increment the iterator till we encounter a nmbr because node value can be of more than one digit\n            while(i<pre.size() && pre[i]>=\'0\'&&pre[i]<=\'9\'&&pre[i]!=\',\')i++;\n            // if here we have an invalid vacancy then preorder is not correct i.e tree cannot be formed out of it\n            if(vac<0)\n                return false;\n            //if the current value is not # then it will contribute 2 vacancy of left and right child hence increase vacancy\n            if(pre[i]!=\'#\')\n                vac+=2;\n        }\n        //if vacancy is still left but string is finished then we will return false\n        if(vac)\n            return false;\n        return true;\n    }
['C', 'C++']