436. Find Right Interval

JIAKAOBO

LeetCode

感谢赞助!

• ㊗️
• 大家
• offer
• 多多！

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;
    }
}