LeetCode - Find Right Interval

Question Definition

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:

1. You may assume the interval’s end point is always bigger than its start point.
2. 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.

### Java Solution
```java
public int[] findRightInterval(Interval[] intervals) {
    TreeMap<Integer, List<Integer>> map = new TreeMap<>();
    for(int i = 0; i < intervals.length; i++){
        Interval interval = intervals[i];
        map.putIfAbsent(interval.start, new LinkedList<>());
        map.get(interval.start).add(i);
    }

    int[] result = new int[intervals.length];
    for(int i = 0; i < intervals.length; i++){
        Interval interval = intervals[i];
        SortedMap<Integer, List<Integer>> tail = map.tailMap(interval.end);
        if(tail.isEmpty()){
            result[i] = -1;
        }else if(tail.firstKey() == interval.end){
            for(int index : map.get(interval.end)){
                if(index != i){
                    result[i] = index;
                    break;
                }
            }
        }else {
            result[i] = map.get(tail.firstKey()).get(0);
        }
    }
    return result;
}