计算2的n次方

淩亂°似流年 2022-05-23 04:09 172阅读 0赞

计算2的N次方  
 时间限制: 1000ms内存限制: 65536kB  
描述  
 任意给定一个正整数N(N<=100)，计算2的N次方的值。  
输入  
 输入只有一个正整数N。  
输出  
 输出2的N次方的值。  
样例输入  
 5  
样例输出  
 32  
参考代码

import java.util.*;
    public class Main {
    	public final static int SIZE = 30;
    	public static void main(String[] args) throws Exception {
    		Scanner cin = new Scanner(System.in);
    		int n = cin.nextInt();
    		int res[] = new int[SIZE + 1];
    		int i;
    		for(i = 0;i < SIZE;++ i){
    			res[i] = 0;
    		}
    		res[0] = 1;
    		while(n > 0){
    			for(i = 0;i < SIZE;++ i){
    				res[i] *= 2;
    			}
    			for(i = 0;i < SIZE;++ i){
    				if(res[i] > 9){
    					res[i + 1] += res[i] / 10;
    					res[i] %= 10;
    				}
    			}
    			n --;
    		}
    		boolean bl = false;
    		StringBuffer bf = new StringBuffer();
    		for(i = SIZE;i >= 0;-- i){
    			if(res[i] != 0 || bl){
    				bf.append(res[i]);
    				bl = true;
    			}
    		}
    		System.out.println(bf);
    	}
    }

根据高位低位改进的代码:

/*
     * Title  :power 2
     * From   :http://blog.csdn.net/binfeihan/article/details/6858655
     * Author :Eric Zhou,binfeihan
     * Email  :binfeihan@126.com
     */
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    public class Main {
    	public static void main(String[] args) throws IOException{
    		BufferedReader cin = new BufferedReader(new InputStreamReader(System.in));
    		int n = Integer.parseInt(cin.readLine().trim());
    		System.out.println(my_power_2(n));
    		//System.out.println(Long.MAX_VALUE);
    		//System.out.println(Long.MIN_VALUE);
    	}
    	public static StringBuffer my_power_2(int N){
    		StringBuffer v = new StringBuffer("");
    		long num[] = new long[2];
    	    num[1] = 1;
    	    if(N > 62){
    	       num[0] = 1;
    	       num[0] = num[0]<<(N - 62);
    	       num[1] = num[1]<<62;
    	       String s = String.valueOf(num[1]);
    	       int size = 30,i = 0,j = 0;
    	       long n[] = new long[size + 1];
    	       //System.out.println(num[0]+" "+s);
    	       for(i = s.length() - 1;i >= 0;-- i){
    	    	   n[j ++] = (long) (num[0] * (s.charAt(i) - '0'));
    	    	   //System.out.println(n[j - 1]);
    	       }
    	       for(i = 0;i < size;++ i){
    	    	   while(n[i] > 9){
    	    		   n[i + 1] += n[i] / 10;
    	    		   n[i] %= 10;
    	    	   }
    	       }
    	       boolean bl = false;
    	       for(i = size;i >= 0;-- i){
    	    	   if(n[i] != 0 || bl){
    	    		   v.append(n[i]);
    	    		   bl = true;
    	    	   }
    	       }
    	    }else{
    	       num[1] = num[1] << N;
    	       v.append(String.valueOf(num[1]));
    	    }   
    	    return v;
    	}
    }