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Problem

You are given an array of intervals, where intervals[i] = [start_i, end_i] and each start_i is unique.

The right interval for an interval i is an interval j such that start_j >= end_i and start_j is minimized. Note that i may equal j.

Return an array of right interval indices for each interval i. If no right interval exists for interval i, then put -1 at index i.

Example 1:

Input: intervals = [[1,2]]
Output: [-1]
Explanation: There is only one interval in the collection, so it outputs -1.


Example 2:

Input: intervals = [[3,4],[2,3],[1,2]]
Output: [-1,0,1]
Explanation: There is no right interval for [3,4].
The right interval for [2,3] is [3,4] since start0 = 3 is the smallest start that is >= end1 = 3.
The right interval for [1,2] is [2,3] since start1 = 2 is the smallest start that is >= end2 = 2.


Example 3:

Input: intervals = [[1,4],[2,3],[3,4]]
Output: [-1,2,-1]
Explanation: There is no right interval for [1,4] and [3,4].
The right interval for [2,3] is [3,4] since start2 = 3 is the smallest start that is >= end1 = 3.


Constraints:

• 1 <= intervals.length <= 2 * 104
• intervals[i].length == 2
• -10^6 <= start_i <= end_i <= 10^6
• The start point of each interval is unique.

Code

class Solution {
public int[] findRightInterval(int[][] intervals) {
TreeMap<Integer, Integer> map = new TreeMap<>();

for(int i = 0; i < intervals.length; i++) {
int[] inter = intervals[i];
map.put(inter[0], i);
}

int[] res = new int[intervals.length];

for(int i = 0; i < intervals.length; i++) {
int[] inter = intervals[i];
Integer ceil = map.ceilingKey(inter[1]);

if(ceil != null){
res[i] = map.get(ceil);
} else {
res[i] = -1;
}
}

return res;
}
}

class Solution {
public int[] findRightInterval(int[][] intervals) {
int len = intervals.length;
int[][] ends = new int[len][2];

for(int i = 0; i < len; i++) {
ends[i] = intervals[i];
}

HashMap<int[], Integer> map = new HashMap<>();

for (int i = 0; i < len; i++) {
map.put(intervals[i], i);
}

Arrays.sort(intervals, (a, b) -> a[0] - b[0]);
Arrays.sort(ends, (a, b) -> a[1] - b[1]);

int j = 0;
int[] res = new int[len];

for (int i = 0; i < len; i++) {
while (j < len && intervals[j][0] < ends[i][1]) {
j++;
}

if(j == len) {
res[map.get(ends[i])] = -1;
} else {
res[map.get(ends[i])] = map.get(intervals[j]);
}
}

return res;
}
}