Leetcode: Find Right Interval

Given a set of intervals, for each of the interval i, check if there exists an interval j whose start point is bigger than or equal to the end point of the interval i, which can be called that j is on the "right" of i.

For any interval i, you need to store the minimum interval j‘s index, which means that the interval j has the minimum start point to build the "right" relationship for interval i. If the interval j doesn‘t exist, store -1 for the interval i. Finally, you need output the stored value of each interval as an array.

Note:
You may assume the interval‘s end point is always bigger than its start point.
You may assume none of these intervals have the same start point.
Example 1:
Input: [ [1,2] ]

Output: [-1]

Explanation: There is only one interval in the collection, so it outputs -1.
Example 2:
Input: [ [3,4], [2,3], [1,2] ]

Output: [-1, 0, 1]

Explanation: There is no satisfied "right" interval for [3,4].
For [2,3], the interval [3,4] has minimum-"right" start point;
For [1,2], the interval [2,3] has minimum-"right" start point.
Example 3:
Input: [ [1,4], [2,3], [3,4] ]

Output: [-1, 2, -1]

Explanation: There is no satisfied "right" interval for [1,4] and [3,4].
For [2,3], the interval [3,4] has minimum-"right" start point.

 1 /**
 2  * Definition for an interval.
 3  * public class Interval {
 4  *     int start;
 5  *     int end;
 6  *     Interval() { start = 0; end = 0; }
 7  *     Interval(int s, int e) { start = s; end = e; }
 8  * }
 9  */
10 public class Solution {
11     public int[] findRightInterval(Interval[] intervals) {
12         if(intervals==null || intervals.length==0) return null;
13         int[] res = new int[intervals.length];
14         TreeMap<Integer, Integer> map = new TreeMap<Integer, Integer>();
15         for (int i=0; i<intervals.length; i++) {
16             map.put(intervals[i].start, i);
17         }
18         for (int i=0; i<intervals.length; i++) {
19             Interval cur = intervals[i];
20             Map.Entry<Integer, Integer> entry = map.higherEntry(cur.end-1);
21             if (entry != null) {
22                 res[i] = entry.getValue();
23             }
24             else res[i] = -1;
25         }
26         return res;
27     }
28 }