240529 볼 모으기

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int n = Integer.parseInt(br.readLine());
	char[] balls = br.readLine().toCharArray();

	int redCount = countColor(balls, 'R');
	int blueCount = n - redCount;

	int leftStreak = countStreak(balls, 0, 1);
	int rightStreak = countStreak(balls, n - 1, -1);

	int minMoves = Math.min(redCount, blueCount);
	minMoves = Math.min(minMoves, calculateMoves(balls, 'R', redCount, leftStreak, rightStreak));
	minMoves = Math.min(minMoves, calculateMoves(balls, 'B', blueCount, leftStreak, rightStreak));

	System.out.println(minMoves);
}

private static int countColor(char[] balls, char color) {
	int count = 0;
	for (char ball : balls) {
		if (ball == color) {
			count++;
		}
	}
	return count;
}

private static int countStreak(char[] balls, int start, int step) {
	int count = 0;
	char initialColor = balls[start];
	for (int i = start; i >= 0 && i < balls.length; i += step) {
		if (balls[i] == initialColor) {
			count++;
		} else {
			break;
		}
	}
	return count;
}

private static int calculateMoves(char[] balls, char color, int colorCount, int leftStreak, int rightStreak) {
	int moves = colorCount;
	if (balls[0] == color) {
		moves = Math.min(moves, colorCount - leftStreak);
	}
	if (balls[balls.length - 1] == color) {
		moves = Math.min(moves, colorCount - rightStreak);
	}
	return moves;
}

출처:https://www.acmicpc.net/problem/17615