字符串左移N位

第一种，简洁算法

根据矩阵运算中的可得

package com.liangyumingblog;

public class RollUpString
{
    private String string;

    public RollUpString(String s)
    {
        this.string = s;
    }

    public String rollup(int n)
    {
        StringBuilder s1 = new StringBuilder(string.substring(0, n));
        StringBuilder s2 = new StringBuilder(string.substring(n + 1));
        return s1.reverse().append(s2.reverse().toString()).reverse().toString();
    }
}

可以不变动实际数组，我们滑动数组指针使得逻辑上看起来是左移了N位

package com.liangyumingblog;

public class RollUpStringCycleList
{
    private char[] string;

    private int begin;

    public RollUpStringCycleList(String s)
    {
        this.string = s.toCharArray();
        this.begin = 0;
        this.end = s.length() - 1;
    }

    public void rollup(int n)
    {
        int localN = n;
        while (localN >= string.length)
        {
            localN -= string.length;
        }
        begin += localN;
        end = begin;
    }

    private int end;

    public boolean hasNext()
    {
        return begin + 1 != end;
    }
    
    public Object next()
    {

        if (begin + 1 == string.length - 1)
        {
            begin = -1;
            return string[string.length - 1];
        }
        return string[++begin];
    }
}

两种不同的实现和使用方式

package com.liangyumingblog;

public class Test
{
    public static void main(String[] s)
    {
        RollUpString rollUpString = new RollUpString("ABCDEFGHIJKF");
        System.out.println(rollUpString.rollup(5));
        RollUpStringCycleList rollUpStringCycleList = new RollUpStringCycleList("ABCDEFGHIJKF");
        rollUpStringCycleList.rollup(5);
        System.out.print(rollUpStringCycleList.next());
        while (rollUpStringCycleList.hasNext())
        {
            System.out.print(rollUpStringCycleList.next());
        }
    }
}

 

GHIJKFABCDE
GHIJKFABCDE
Process finished with exit code 0