algorithm-class/体系学习班/class47/Code01_StrangePrinter.java

package class47;

// 本题测试链接 : https://leetcode.com/problems/strange-printer/
public class Code01_StrangePrinter {

	public static int strangePrinter1(String s) {
		if (s == null || s.length() == 0) {
			return 0;
		}
		char[] str = s.toCharArray();
		return process1(str, 0, str.length - 1);
	}

	// 要想刷出str[L...R]的样子！
	// 返回最少的转数
	public static int process1(char[] str, int L, int R) {
		if (L == R) {
			return 1;
		}
		// L...R
		int ans = R - L + 1;
		for (int k = L + 1; k <= R; k++) {
			// L...k-1 k....R
			ans = Math.min(ans, process1(str, L, k - 1) + process1(str, k, R) - (str[L] == str[k] ? 1 : 0));
		}
		return ans;
	}

	public static int strangePrinter2(String s) {
		if (s == null || s.length() == 0) {
			return 0;
		}
		char[] str = s.toCharArray();
		int N = str.length;
		int[][] dp = new int[N][N];
		return process2(str, 0, N - 1, dp);
	}

	public static int process2(char[] str, int L, int R, int[][] dp) {
		if (dp[L][R] != 0) {
			return dp[L][R];
		}
		int ans = R - L + 1;
		if (L == R) {
			ans = 1;
		} else {
			for (int k = L + 1; k <= R; k++) {
				ans = Math.min(ans, process2(str, L, k - 1, dp) + process2(str, k, R, dp) - (str[L] == str[k] ? 1 : 0));
			}
		}
		dp[L][R] = ans;
		return ans;
	}

	public static int strangePrinter3(String s) {
		if (s == null || s.length() == 0) {
			return 0;
		}
		char[] str = s.toCharArray();
		int N = str.length;
		int[][] dp = new int[N][N];
		dp[N - 1][N - 1] = 1;
		for (int i = 0; i < N - 1; i++) {
			dp[i][i] = 1;
			dp[i][i + 1] = str[i] == str[i + 1] ? 1 : 2;
		}
		for (int L = N - 3; L >= 0; L--) {
			for (int R = L + 2; R < N; R++) {
				dp[L][R] = R - L + 1;
				for (int k = L + 1; k <= R; k++) {
					dp[L][R] = Math.min(dp[L][R], dp[L][k - 1] + dp[k][R] - (str[L] == str[k] ? 1 : 0));
				}
			}
		}
		return dp[0][N - 1];
	}

}