Strobogrammatic Number III in C++

Suppose we want to define a function to count the total strobogrammatic numbers that exist in the range of (low and high). As we know that a strobogrammatic number is a number that looks the same when rotated 180 degrees.

So, if the input is like low = "50", high = "100", then the output will be 3 as there are three results, 69, 88, and 96.

To solve this, we will follow these steps −

• Define a function findStrobogrammatic(), this will take n,

• Define an array ret

• if n & 1 is non-zero, then −

  • insert "0" at the end of ret

  • insert "1" at the end of ret

  • insert "8" at the end of ret

• Otherwise

  • insert blank string at the end of ret

• for n > 1, update n := n - 2, do −

  • Define an array temp

  • for initialize i := 0, when i < size of ret, update (increase i by 1), do −

    • s := ret[i]

    • if n > 3, then −

      • insert "0" + s + "0" at the end of temp

    • insert "1" + s + "1" at the end of temp

    • insert "8" + s + "8" at the end of temp

    • insert "6" + s + "9" at the end of temp

    • insert "9" + s + "6" at the end of temp

  • ret := temp

• return ret

• From the main method, do the following −

• ret := 0

• Define an array v

• for initialize i := size of low, when i <= size of high, update (increase i by 1), do −

  • v := findStrobogrammatic(i)

  • for initialize j := 0, when j < size of v, update (increase j by 1), do −

    • ret := ret + (1 when length of v[j] > length of low AND length of high > length of v[j])

• return ret

Example

Let us see the following implementation to get better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
   vector<string> findStrobogrammatic(int n) {
      vector<string> ret;
      if (n & 1) {
         ret.push_back("0");
         ret.push_back("1");
         ret.push_back("8");
      }
      else {
         ret.push_back("");
      }
      for (; n > 1; n -= 2) {
         vector<string> temp;
         for (int i = 0; i < ret.size(); i++) {
            string s = ret[i];
            if (n > 3) {
               temp.push_back("0" + s + "0");
            }
            temp.push_back("1" + s + "1");
            temp.push_back("8" + s + "8");
            temp.push_back("6" + s + "9");
            temp.push_back("9" + s + "6");
         }
         ret = temp;
      }
      return ret;
   }
   bool compare(string a, string b){
      return a.size() == b.size() ? a >= b : a.size() > b.size();
   }
   int strobogrammaticInRange(string low, string high) {
      int ret = 0;
      vector<string> v;
      for (int i = low.size(); i <= high.size(); i++) {
         v = findStrobogrammatic(i);
         for (int j = 0; j < v.size(); j++) {
            ret += compare(v[j], low) && compare(high, v[j]);
         }
      }
      return ret;
   }
};
main(){
   Solution ob;
   cout <<(ob.strobogrammaticInRange("50", "100"));
}

Input

"50","100"

Output

3