Problem:
Score : 300 points

Problem Statement

There are N stones arranged in a row. Every stone is painted white or black.
A string S represents the color of the stones. The i-th stone from the left is white if the i-th character of S is ., and the stone is black if the character is #.

Takahashi wants to change the colors of some stones to black or white so that there will be no white stone immediately to the right of a black stone.
Find the minimum number of stones that needs to be recolored.

Constraints

1 \leq N \leq 2\times 10^5

S is a string of length N consisting of . and #.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print the minimum number of stones that needs to be recolored.

Sample Input 1

3
#.#

Sample Output 1

1

It is enough to change the color of the first stone to white.

Sample Input 2

5
#.##.

Sample Output 2

2

Sample Input 3

9
.........

Sample Output 3

0

Solution in C++14 (Clang 3.8.0) (judge verdict: Wrong Answer)


#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
#include <queue>
#include <string>
using namespace std;

int countdot(int start,int N,string S){
  int c=0;
  for(int i=start;i<N;i++){
    if(S[i]=='.'){
      c++;
    }
  }
  return c;
}
int counts(int start,int N,string S){
  int c=0;
  for(int i=start;i<N;i++){
    if(S[i]=='#'){
      c++;
    }
  }
  return c;
}
int main(){
  int N;
  string S;
  cin>>N>>S;
  int index[N];
  for(int i=0;i<N;i++){
    index[i]=0;
  }
  int c=0;
  while(c<N){
    if(S[c]=='#'){
      index[c]=c;
    }
    c++;
  }
  int ans = N;
  int d=0;
  bool flag = false;
  for(int x : index){
    if(x!=0){
      flag=true;
      ans = min(ans,d+countdot(x,N,S));
      d++;
    }
  }
  ans = min(d,ans);
  if(flag){
    cout<<ans<<"\n";
  }else{
    cout<<0<<"\n";
  }
}