lintcode-medium-Number of Airplanes in the Sky

Given an interval list which are flying and landing time of the flight. How many airplanes are on the sky at most?

 

 Notice

If landing and flying happens at the same time, we consider landing should happen at first.

Example

For interval list

[
  [1,10],
  [2,3],
  [5,8],
  [4,7]
]

Return 3

 

/**
 * Definition of Interval:
 * public classs Interval {
 *     int start, end;
 *     Interval(int start, int end) {
 *         this.start = start;
 *         this.end = end;
 *     }
 */

class Solution {
    /**
     * @param intervals: An interval array
     * @return: Count of airplanes are in the sky.
     */
    public int countOfAirplanes(List<Interval> airplanes) { 
        // write your code here
        
        if(airplanes == null || airplanes.size() == 0)
            return 0;
        
        ArrayList<point> list = new ArrayList<point>();
        
        for(Interval interval: airplanes){
            list.add(new point(interval.start, 1));
            list.add(new point(interval.end, 0));
        }
        
        Collections.sort(list, new Comparator<point>(){
            public int compare(point p1, point p2){
                if(p1.time == p2.time){
                    return p1.flag - p2.flag;
                }
                else{
                    return p1.time - p2.time;
                }
            } 
        });
        
        int count = 0;
        int ans = 0;
        
        for(point p: list){
            if(p.flag == 1)
                count++;
            else
                count--;
            
            ans = Math.max(ans, count);
        }
        
        return ans;
    }
    
    class point{
        int time;
        int flag;
        
        public point(int time, int flag){
            this.time = time;
            this.flag = flag;
        }
    }
    
}