Java实现 洛谷 P1582 倒水

import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
 
public class Main {
	static long m = 0, f = 0;
	public static void main(String[] args) {
		FastScanner fs = new FastScanner();
		int a = fs.nextInt();
		int b = fs.nextInt();
		long x[] = new long[32];
		boolean y[] = new boolean[32];
		int n = 0;
		x[0] = 1;
		x[1] = 2;
		for (int i = 2; i < y.length; i++) {
			x[i] = 2 * x[i - 1];
		}
		for (int i = 31; i >= 0; i--) {
			if (a >= x[i]) {
				a -= x[i];
				y[i] = true;
				n++;
			}
		}
		if (n > b) {
			int d = n - b;
			for (int i = 0; i < y.length; i++) {
				if (y[i] && d == 0) {
					f = x[i];
					break;
				}
				if (y[i] && d != 0) {
					m += x[i];
					d--;
				}
			}
			System.out.println(f - m);
		} else {
			System.out.println(0);
		}
 
	}
 
	public static class FastScanner {
		private BufferedReader br;
		private StringTokenizer st;
 
		public FastScanner() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}
 
		public String nextToken() {
			while (st == null || !st.hasMoreElements()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception e) {
 
				}
 
			}
			return st.nextToken();
		}
 
		public int nextInt() {
			return Integer.valueOf(nextToken());
		}
	}
 
}