區間合併

題目描述：給出多組區間，求所有區間的交集

輸入描述：多個區間，單個區間用逗號隔開，區間之間用空格隔開，例如：2,6 3,8 6,9

輸出描述：將合併後的區間輸出，例如2,6 3,8 6,9合併後輸出2,9    1,3 2,6 8,10合併後輸出1,6 8,10

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Scanner;

/*
class Interval {
int start,end;
	public Interval(int start, int end) {
		this.start = start;
	    this.end = end;
	}
}
*/
public class Test2 {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		List<Interval> list=new ArrayList<>();
		String[] s=str.split(" ");
		for (int i = 0; i < s.length; i++) {
			String[] s1=s[i].split(",");
			Interval interval=new Interval(Integer.valueOf(s1[0]),Integer.valueOf(s1[1]));
			list.add(interval);
		}
		List<Interval> list1=new ArrayList<>();
		list1=merge(list);
		Iterator<Interval> it=list1.iterator();
		while(it.hasNext()){
			Interval inter=it.next();
			if(it.hasNext()==false) System.out.println(inter.start+","+inter.end);
			else System.out.print(inter.start+","+inter.end+" ");
		}
	}

	  public static List<Interval> merge(List<Interval> intervals) {
	        List<Interval> intervals1 = new ArrayList<>();
	        if (intervals.size() == 0) {
	            return intervals;
	        }
	        for (int i = 0; i < intervals.size(); i++) {
	            for (int j = i+1; j < intervals.size(); j++) {
	                if (intervals.get(i).start > intervals.get(j).start) {
	                    Interval tem = intervals.get(i);
	                    intervals.set(i,intervals.get(j));
	                    intervals.set(j,tem);
	                }
	            }
	        }
	        int min = intervals.get(0).start;
	        int max = intervals.get(0).end;
	        for (int i = 1; i < intervals.size(); i++) {
	            //重疊即合併區間
	            if (intervals.get(i).start <= max) {
	                max = intervals.get(i).end > max ? intervals.get(i).end : max;
	            } else {
	                intervals1.add(new Interval(min,max));
	                min = intervals.get(i).start;
	                max = intervals.get(i).end;
	            }
	        }
	        intervals1.add(new Interval(min,max));
	        return intervals1;
	    }

}
 

連結串列解法

import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import java.util.LinkedList;
import java.util.Scanner;

class Interval {
int start,end;
	public Interval(int start, int end) {
		this.start = start;
	    this.end = end;
	}
}
public class Main {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		String str=sc.nextLine();
		List<Interval> list=new LinkedList<>();
		String[] s=str.split(" ");
		for (int i = 0; i < s.length; i++) {
			String[] s1=s[i].split(",");
			Interval interval=new Interval(Integer.valueOf(s1[0]),Integer.valueOf(s1[1]));
			list.add(interval);
		}
		list=merge(list);
		Iterator<Interval> it=list.iterator();
		while(it.hasNext()){
			Interval inter=it.next();
			if(it.hasNext()==false) System.out.println(inter.start+","+inter.end);
			else System.out.print(inter.start+","+inter.end+" ");
		}
	}
	  public static List<Interval> merge(List<Interval> intervals) {
	     List<Interval> result = new LinkedList<>();

        if (intervals == null || intervals.size() < 1) {
            return result;
        }

        // 先對區間進行排序，使用一個匿名內部類
        Collections.sort(intervals, new Comparator<Interval>() {
            @Override
            public int compare(Interval o1, Interval o2) {
                return o1.start - o2.start;
            }
        });

        // 排序後，後一個元素（記為next）的start一定是不小於前一個（記為prev）start的，
        // 對於新加入的區間，假設next.start大於prev.end就說明這兩個區間是分開的，要添
        // 加一個新的區間。否則說明next.start在[prev.start, prev.end]內。則僅僅要看
        // next.end是否是大於prev.end，假設大於就要合併區間（擴大）
        Interval prev = null;
        for (Interval item : intervals) {

            if (prev == null || prev.end < item.start) {
                result.add(item);
                prev = item;
            } else if (prev.end < item.end) {
                prev.end = item.end;
            }
        }

        return result;
	    }

}