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 Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)



import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(final String[] args) {

        try (final Scanner sc = new Scanner(System.in)) {
            int N = sc.nextInt();
            String S = sc.next();
            List<Integer> counts = new ArrayList<>();
            char prev = S.charAt(0);
            int length = 1;
            for (int i = 1; i < N; i++) {
                if (prev == S.charAt(i)) {
                    length++;
                } else {
                    counts.add(length);
                    length = 1;
                }
                prev = S.charAt(i);
            }
            counts.add(length);

            int result = 0;
            boolean bExists = false;
            for (int i = (S.charAt(0) == '#' ? 0 : 1); i < counts.size(); i += 2) {
                if ((i + 1) < counts.size()) {
                    int b = counts.get(i);
                    int w = counts.get(i + 1);
                    if (!bExists && b <= w) {
                        result += b;
                    } else {
                        result += w;
                        bExists = true;
                    }
                }
            }
            System.out.println(result);
        }
    }

}