微软2014实习生及秋令营技术类职位在线测试-题目2 : K-th string

Description

Consider a string set that each of them consists of {0, 1} only. All strings in the set have the same number of 0s and 1s. Write a program to find and output the K-th string according to the dictionary order. If such a string doesn’t exist, or the input is not valid, please output “Impossible”. For example, if we have two ‘0’s and two ‘1’s, we will have a set with 6 different strings, {0011, 0101, 0110, 1001, 1010, 1100}, and the 4th string is 1001.

Input

The first line of the input file contains a single integer t (1 ≤ t ≤ 10000), the number of test cases, followed by the input data for each test case.
Each test case is 3 integers separated by blank space: N, M(2 <= N + M <= 33 and N , M >= 0), K(1 <= K <= 1000000000). N stands for the number of ‘0’s, M stands for the number of ‘1’s, and K stands for the K-th of string in the set that needs to be printed as output.

Output

For each case, print exactly one line. If the string exists, please print it, otherwise print “Impossible”.

样例输入

3
2 2 2
2 2 7
4 7 47

样例输出

0101Impossible01010111011

我的解答： 

package Kthstring;

import java.io.BufferedInputStream;
import java.util.Scanner;

public class Main {
	public static int jc(int n) {
		if (n > 1)
			return n * jc(n - 1);
		else
			return 1;
	}

	public static void main(String[] args) {
		Scanner cin = new Scanner(new BufferedInputStream(System.in));
		int num = cin.nextInt();
		cin.nextLine();
		int tem = 0;
		while (tem < num) {
			int n = cin.nextInt();
			int m = cin.nextInt();
			int t = cin.nextInt();

			int total = jc(n + m) / jc(n) / jc(m);
			if (total < t)
				System.out.println("Impossible");
			else {
				int count = 1;
				int a = (int) (Math.pow(2, m) - 1);
				String s = Integer.toBinaryString(a);

				while (count < t) {
					a = a + 1;
					s = Integer.toBinaryString(a);
					int i = 0;
					for (int j = 0; j < s.length(); j++) {
						char c = s.charAt(j);
						if (c == ‘1‘)
							i++;
					}
					if (i == m)
						count++;
				}

				for (; s.length() < (n + m);)
					s = "0" + s;
				System.out.println(s);
			}
			tem++;
		}
	}

}

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微软2014实习生及秋令营技术类职位在线测试-题目2 : K-th string

原文：http://blog.csdn.net/lsp1991/article/details/23555447