Find Right Interval

描述

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.

题解

package algorithms

import (
	"github.com/ljun20160606/leetcode/algorithms"
	"sort"
)

type Interval = algorithms.Interval

/**
 * Definition for an interval.
 * type Interval struct {
 *	   Start int
 *	   End   int
 * }
 */
func findRightInterval(intervals []Interval) []int {
	size := len(intervals)

	starts := make([]int, size)
	idxs := make(map[int]int, size)
	res := make([]int, size)

	for i, v := range intervals {
		starts[i] = v.Start
		idxs[v.Start] = i
	}

	sort.Ints(starts)

	for i, v := range intervals {
		idx := sort.SearchInts(starts, v.End)
		if idx < size {
			res[i] = idxs[starts[idx]]
		} else {
			res[i] = -1
		}
	}

	return res
}