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