MergeInterval.java

package learn.freq05;

import entity.Interval;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

//Given a collection of intervals, merge all overlapping intervals.
//
//For example,
//Given [1,3],[2,6],[8,10],[15,18],
//return [1,6],[8,10],[15,18].   
//其实只有 第一和第二个数组融合了

//题目给你的interval都是start小 end大

//merge 间隔
public class MergeInterval {

    public ArrayList<Interval> merge(ArrayList<Interval> intervals) {
        ArrayList<Interval> result = new ArrayList<Interval>();
        if (intervals == null || intervals.size() <= 1) {
            return intervals;
        }

        Collections.sort(intervals, new IntervalComparator());
        //排序好 后
        //弄一个 prev=0位 然后 和从1遍历的curr比
        //如果curr.start>=prev.end 说明有 interval
        //那时候只要在比较prev.end和curr.end 那个end 大就更新prev.edm
        //如果 curr.start<prev.end  说明没有interval
        //直接   result.add(prev); prev=curr;
        //循环结束后再加一次即可

        Interval prev = intervals.get(0);
        for (int i = 1; i < intervals.size(); i++) {

            Interval curr = intervals.get(i);
            if (curr.start <= prev.end) {
                if (prev.end < curr.end) {
                    prev.end = curr.end;
                }
            } else {
                result.add(prev);
                prev = curr;
            }
        }
        result.add(prev);
        return result;
    }

    static class IntervalComparator implements Comparator<Interval> {
        public int compare(Interval o1, Interval o2) {
            if (o1.start < o2.start) {
                return -1;
            }
            if (o1.start > o2.start) {
                return 1;
            }
            return 0;
        }
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

    }

}

// leetcode 不认类的comparator