algorithm-class/体系学习班/class39/Code03_10Ways.java

package class39;

import java.util.LinkedList;

public class Code03_10Ways {

	public static long ways1(int N) {
		int zero = N;
		int one = N;
		LinkedList<Integer> path = new LinkedList<>();
		LinkedList<LinkedList<Integer>> ans = new LinkedList<>();
		process(zero, one, path, ans);
		long count = 0;
		for (LinkedList<Integer> cur : ans) {
			int status = 0;
			for (Integer num : cur) {
				if (num == 0) {
					status++;
				} else {
					status--;
				}
				if (status < 0) {
					break;
				}
			}
			if (status == 0) {
				count++;
			}
		}
		return count;
	}

	public static void process(int zero, int one, LinkedList<Integer> path, LinkedList<LinkedList<Integer>> ans) {
		if (zero == 0 && one == 0) {
			LinkedList<Integer> cur = new LinkedList<>();
			for (Integer num : path) {
				cur.add(num);
			}
			ans.add(cur);
		} else {
			if (zero == 0) {
				path.addLast(1);
				process(zero, one - 1, path, ans);
				path.removeLast();
			} else if (one == 0) {
				path.addLast(0);
				process(zero - 1, one, path, ans);
				path.removeLast();
			} else {
				path.addLast(1);
				process(zero, one - 1, path, ans);
				path.removeLast();
				path.addLast(0);
				process(zero - 1, one, path, ans);
				path.removeLast();
			}
		}
	}

	public static long ways2(int N) {
		if (N < 0) {
			return 0;
		}
		if (N < 2) {
			return 1;
		}
		long a = 1;
		long b = 1;
		long limit = N << 1;
		for (long i = 1; i <= limit; i++) {
			if (i <= N) {
				a *= i;
			} else {
				b *= i;
			}
		}
		return (b / a) / (N + 1);
	}

	public static void main(String[] args) {
		System.out.println("test begin");
		for (int i = 0; i < 10; i++) {
			long ans1 = ways1(i);
			long ans2 = ways2(i);
			if (ans1 != ans2) {
				System.out.println("Oops!");
			}
		}
		System.out.println("test finish");
	}

}