求有序整数集合a和b的交集函数

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本文提供三种不同的Java实现方法来寻找两个有序整数数组的交集，包括使用双重循环、改进的单循环及利用HashSet的数据结构特性。

问题描述：

有两个有序整数集合a和b，写一个函数找出它们的交集？

几种解决方案：

一：

import java.util.Arrays; 

public class Test { 

    public static void main(String args[]){ 
        int[] b = {4, 6, 7, 7, 7, 7, 8, 8, 9, 10, 100, 130, 130, 140, 150}; 
        int[] a = {2, 3, 4, 4, 4, 4, 7, 8, 8, 8, 8, 9, 100, 130, 150, 160}; 
        int[] c = intersect(a, b); 
        System.out.println(Arrays.toString(c)); 
    } 

    public static int[] intersect(int[] a, int[] b) { 
        if(a[0] > b[b.length - 1] || b[0] > a[a.length - 1]) { 
            return new int[0]; 
        } 
        int[] intersection = new int[Math.max(a.length, b.length)]; 
        int offset = 0; 
        for(int i = 0, s = i; i < a.length && s < b.length; i++) { 
            while(a[i] > b[s]) { 
                s++; 
            } 
            if(a[i] == b[s]) { 
                intersection[offset++] = b[s++]; 
            } 
            while(i < (a.length - 1) && a[i] == a[i + 1]) { 
                i++; 
            } 
        } 
        if(intersection.length == offset) { 
            return intersection; 
        } 
        int[] duplicate = new int[offset]; 
        System.arraycopy(intersection, 0, duplicate, 0, offset); 
        return duplicate; 
    } 
}

import java.util.ArrayList; 

public class jiaoji { 

    public static void main(String[] args) { 
        // TODO Auto-generated method stub 
        int[] b = { 4, 6, 7, 7, 7, 8, 8, 9, 10, 100, 130, 140, 150 }; 
        int[] a = { 2, 3, 4, 4, 4, 7, 8, 8, 8, 8, 9, 100, 130, 150, 160 }; 
        ArrayList c = sect(a, b); 
        for (int i = 0; i < c.size(); i++) { 
            System.out.print(c.get(i) + ","); 
        } 
    } 

    public static ArrayList sect(int[] a, int[] b) { 
        int k = 0; 
        int startposb = 0; 

        if (a[0] > b[b.length - 1] || b[0] > a[a.length - 1]) { 
            return new ArrayList(); 
        } 
        ArrayList arraylist = new ArrayList(); 
        for (int i = 0; i < a.length; i++) { 
            for (int j = startposb; j < b.length; j++) { 
                if (a[i] == b[j]) { 
                    arraylist.add(k, a[i]); 
                    k++; 
                    startposb = j + 1; 
                    break; 
                } 
            } 
        } 
        return arraylist; 
    } 
}

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

public class NumberCross { 

    public static void main(String[] args) { 
        int a[] = {1,3,4,5,6,7,499,199}; 
        int b[] = {3,299,199,8,9,499}; 
        Set<Integer> list = new HashSet<Integer>(); 
        for(int i=0; i<a.length; i++) { 
            list.add(a[i]); 
        } 
        for(int j=0; j<b.length; j++) { 
            list.add(b[j]); 
        } 
        for(Iterator<Integer> iter=list.iterator(); iter.hasNext();) { 
            System.out.print(iter.next() + " "); 
        } 
    } 
}