436. Find Right Interval

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

The right interval for an interval i is an interval j such that startj >= endi and startj is minimized.

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
  • -106 <= starti <= endi <= 106
  • The start point of each interval is unique.

Rust Solution

struct Solution;
use std::collections::BTreeMap;

impl Solution {
    fn find_right_interval(intervals: Vec<Vec<i32>>) -> Vec<i32> {
        let n = intervals.len();
        let mut res: Vec<i32> = vec![-1; n];
        let mut btm: BTreeMap<i32, usize> = BTreeMap::new();
        for i in 0..n {
            let l = intervals[i][0];
            btm.insert(l, i);
        }
        for i in 0..n {
            let r = intervals[i][1];
            for (_, &j) in btm.range(r..).take(1) {
                res[i] = j as i32;
            }
        }
        res
    }
}

#[test]
fn test() {
    let intervals = vec_vec_i32![[1, 2]];
    let res = vec![-1];
    assert_eq!(Solution::find_right_interval(intervals), res);
    let intervals = vec_vec_i32![[3, 4], [2, 3], [1, 2]];
    let res = vec![-1, 0, 1];
    assert_eq!(Solution::find_right_interval(intervals), res);
    let intervals = vec_vec_i32![[1, 4], [2, 3], [3, 4]];
    let res = vec![-1, 2, -1];
    assert_eq!(Solution::find_right_interval(intervals), res);
}

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