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.*;
public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        String S = sc.next();
        int[][] dp = new int[S.length()][2];
        
        if (S.charAt(0)=='.') {
            dp[0][0] = 0;
            dp[0][1] = 1;
        } else if (S.charAt(0)=='#') {
            dp[0][0] = 1;
            dp[0][1] = 0;
        }
        for (int i=1;i<S.length();++i){
            if (S.charAt(0)=='.') {
                dp[i][0] = dp[i-1][0];
                dp[i][1] = Math.min(dp[i-1][0],dp[i-1][1])+1;
            } else if (S.charAt(0)=='#') {
                dp[i][0] = dp[i-1][0]+1;
                dp[i][1] = Math.min(dp[i-1][0],dp[i-1][1]);
            }
        }
        int ans = Math.min(dp[dp.length-1][0],dp[dp.length-1][1]);
        System.out.println(ans);
    }
    
}