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436. Find Right Interval

Description

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

Solutions

Binary search.

• Java
• C++
• Python
• Go
• TypeScript

• class Solution {
      public int[] findRightInterval(int[][] intervals) {
          int n = intervals.length;
          List<int[]> starts = new ArrayList<>();
          for (int i = 0; i < n; ++i) {
              starts.add(new int[] {intervals[i][0], i});
          }
          starts.sort(Comparator.comparingInt(a -> a[0]));
          int[] res = new int[n];
          int i = 0;
          for (int[] interval : intervals) {
              int left = 0, right = n - 1;
              int end = interval[1];
              while (left < right) {
                  int mid = (left + right) >> 1;
                  if (starts.get(mid)[0] >= end) {
                      right = mid;
                  } else {
                      left = mid + 1;
                  }
              }
              res[i++] = starts.get(left)[0] < end ? -1 : starts.get(left)[1];
          }
          return res;
      }
  }
  

• class Solution {
  public:
      vector<int> findRightInterval(vector<vector<int>>& intervals) {
          int n = intervals.size();
          vector<pair<int, int>> starts;
          for (int i = 0; i < n; ++i) {
              starts.emplace_back(make_pair(intervals[i][0], i));
          }
          sort(starts.begin(), starts.end());
          vector<int> res;
          for (auto interval : intervals) {
              int left = 0, right = n - 1;
              int end = interval[1];
              while (left < right) {
                  int mid = left + right >> 1;
                  if (starts[mid].first >= end)
                      right = mid;
                  else
                      left = mid + 1;
              }
              res.push_back(starts[left].first < end ? -1 : starts[left].second);
          }
          return res;
      }
  };
  

• class Solution:
      def findRightInterval(self, intervals: List[List[int]]) -> List[int]:
          for i, v in enumerate(intervals):
              v.append(i)
          intervals.sort()
          n = len(intervals)
          ans = [-1] * n
          for _, e, i in intervals:
              j = bisect_left(intervals, [e])
              if j < n:
                  ans[i] = intervals[j][2]
          return ans
  
  

• func findRightInterval(intervals [][]int) []int {
  	n := len(intervals)
  	starts := make([][]int, n)
  	for i := 0; i < n; i++ {
  		starts[i] = make([]int, 2)
  		starts[i][0] = intervals[i][0]
  		starts[i][1] = i
  	}
  	sort.Slice(starts, func(i, j int) bool {
  		return starts[i][0] < starts[j][0]
  	})
  	var res []int
  	for _, interval := range intervals {
  		left, right, end := 0, n-1, interval[1]
  		for left < right {
  			mid := (left + right) >> 1
  			if starts[mid][0] >= end {
  				right = mid
  			} else {
  				left = mid + 1
  			}
  		}
  		val := -1
  		if starts[left][0] >= end {
  			val = starts[left][1]
  		}
  		res = append(res, val)
  	}
  	return res
  }
  

• function findRightInterval(intervals: number[][]): number[] {
      const n = intervals.length;
      const starts = Array.from({ length: n }).map(() => new Array<number>(2));
      for (let i = 0; i < n; i++) {
          starts[i][0] = intervals[i][0];
          starts[i][1] = i;
      }
      starts.sort((a, b) => a[0] - b[0]);
  
      return intervals.map(([_, target]) => {
          let left = 0;
          let right = n;
          while (left < right) {
              const mid = (left + right) >>> 1;
              if (starts[mid][0] < target) {
                  left = mid + 1;
              } else {
                  right = mid;
              }
          }
          if (left >= n) {
              return -1;
          }
          return starts[left][1];
      });
  }
  
  

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