Head_Tail_Swap.cpp

// Umesh is a Mathematician,
// He is given a task to his student Shanker, 
// There are N coins in a row, indexed from 0 to N-1, intially all the coins are 
// facing "tail". And Umesh has given him a final State-to-Achieve.

// Shanker can achieve the final state by doing a swap operation as follows:
//     - Shanker can choose any index i, 
//     - all the coins has to be swap their faces, from "head" to "tail" 
//     or "tail to "head" from index 'i' to 'N-1'.

// Shanker is given a binary string S, State-to-Achieve contains [0,1] only. 
// "tail" indicates with '0' and "head" indicates with '1'

// Please help Shanker to find the minimum number of swap operations required 
// to reach State-to-Achieve.


// Input Format:
// -------------
// A String S, final State-to-Achieve.

// Output Format:
// --------------
// Print an integer, minimum number of swap operations.


// Sample Input-1:
// ---------------
// 10111010

// Sample Output-1:
// ----------------
// 6

// Explanation: 
// ------------
// Initial configuration "00000000".
// swap from the first coin: "00000000" -> "11111111"
// swap from the second coin: "11111111" -> "10000000"
// swap from the third coin: "10000000" -> "10111111"
// swap from the sixth coin: "10111111" -> "10111000"
// swap from the seventh coin: "10111000" -> "10111011"
// swap from the eighth coin: "10111011" -> "10111010"
// A total of 6 swap operations required.


// Sample Input-2:
// ---------------
// 11111

// Sample Output-2:
// ----------------
// 1





#include<bits/stdc++.h>
using namespace std;
int main(){
    string s;
    cin>>s;
    int res=0;
    bool state=false;
    for(auto i:s){
        if((i=='0' && state==true) || (i=='1' && state==false)){
            res++;
            if(state==true){
                state=false;
            }
            else{
                state=true;
            }
        }
    }
    cout<<res;
}