小猴爬台阶问题：

    有一仅仅小猴非常顽皮，喜欢爬台阶，但因为小猴太小，所以它仅仅能一步爬1个或2个台阶。请计算该小猴全部可能的爬行路径。

package shuai.study.steps;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

/**
 * @author shengshu
 * 
 */
public class MonkeyCrawl {

	// Get paths, which will be permutated
	public static Set<String> getPathsSet(int steps) {
		Set<String> pathsSet = new HashSet<String>();

		for (int i = 0; i <= steps / 2; i++) {
			int twoStepSum = i * 2;
			int oneStepTimes = steps - twoStepSum;

			StringBuffer pathStringBuffer = new StringBuffer();

			for (int x = 0; x < oneStepTimes; x++) {
				// "-" represent one step
				pathStringBuffer.append("-");
			}

			for (int y = 0; y < i; y++) {
				// "=" represent two steps
				pathStringBuffer.append("=");
			}

			pathsSet.add(pathStringBuffer.toString());
		}

		return pathsSet;
	}

	// Permutate all possible paths
	public static void permutatePaths(String path, List<String> list) {
		if (path.length() == 1) {
			for (int i = 0; i < list.size(); i++) {
				System.out.print(list.get(i));
			}

			System.out.println(path);
		} else {
			int index[] = new int[path.length()];

			for (int i = 0; i < index.length; i++) {
				index[i] = path.indexOf(path.charAt(i));
			}

			for (int i = 0; i < path.length(); i++) {
				String subPath = path.substring(1, path.length());

				if (i == index[i]) {
					list.add("" + path.charAt(0));

					permutatePaths(subPath, list);

					list.remove(list.size() - 1);
				}

				path = subPath + path.charAt(0);
			}
		}
	}

	public static void main(String[] args) {
		// Set steps as 15, or others
		Set<String> pathsSet = MonkeyCrawl.getPathsSet(15);

		Iterator<String> iterator = pathsSet.iterator();
		while (iterator.hasNext()) {
			String path = iterator.next();
			MonkeyCrawl.permutatePaths(path, new ArrayList<String>());
		}
	}

}