[LeetCode51]Merge Intervals

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].

Analysis:

The idea is simple. First sort the vector according to the start value. Second, scan every interval, if it can be merged to the previous one, then merge them, else push it into the result vector.

Note here:
The use of std::sort to sort the vector, need to define a compare function, which need to be static. (static bool myfunc() ) The sort command should be like this: std::sort(intervals.begin,intervals.end, Solution::myfunc); otherwise, it won't work properly.

For java, we need to write own compartor implements compartor interface.

Java

public class Solution {
    class IntervalCompartor implements Comparator<Interval>{

		@Override
		public int compare(Interval o1, Interval o2) {
			// TODO Auto-generated method stub
			return o1.start-o2.start;
		}
		
	}
	public List<Interval> merge(List<Interval> intervals) {
        List<Interval> result = new ArrayList<>();
        if(intervals.size()<=1) return intervals;
        Collections.sort(intervals, new IntervalCompartor());
        result.add(intervals.get(0));
        for(int i=1;i<intervals.size();i++){
        	Interval tem = result.get(result.size()-1);
        	if(tem.end>=intervals.get(i).start){
        		tem.end = Math.max(tem.end, intervals.get(i).end);
        		result.set(result.size()-1, tem);
        	}else {
				result.add(intervals.get(i));
			}
        }
        return result;
    }
}

c++

public class Solution {
    class IntervalCompartor implements Comparator<Interval>{

		@Override
		public int compare(Interval o1, Interval o2) {
			// TODO Auto-generated method stub
			return o1.start-o2.start;
		}
		
	}
	public List<Interval> merge(List<Interval> intervals) {
        List<Interval> result = new ArrayList<>();
        if(intervals.size()<=1) return intervals;
        Collections.sort(intervals, new IntervalCompartor());
        result.add(intervals.get(0));
        for(int i=1;i<intervals.size();i++){
        	Interval tem = result.get(result.size()-1);
        	if(tem.end>=intervals.get(i).start){
        		tem.end = Math.max(tem.end, intervals.get(i).end);
        		result.set(result.size()-1, tem);
        	}else {
				result.add(intervals.get(i));
			}
        }
        return result;
    }
}