An integer interval [a, b]
(for integers a < b
) is a set of all consecutive integers from a
to b
, including a
and b
.
Find the minimum size of a set S such that for every integer interval A in intervals
, the intersection of S with A has size at least 2.
Example 1:
Input: intervals = [[1, 3], [1, 4], [2, 5], [3, 5]] Output: 3 Explanation: Consider the set S = {2, 3, 4}. For each interval, there are at least 2 elements from S in the interval. Also, there isn't a smaller size set that fulfills the above condition. Thus, we output the size of this set, which is 3.
Example 2:
Input: intervals = [[1, 2], [2, 3], [2, 4], [4, 5]] Output: 5 Explanation: An example of a minimum sized set is {1, 2, 3, 4, 5}.
Note:
intervals
will have length in range[1, 3000]
.intervals[i]
will have length2
, representing some integer interval.intervals[i][j]
will be an integer in[0, 10^8]
.
Approach #1: C++. [greedy]
class Solution { public: int intersectionSizeTwo(vector<vector<int>>& intervals) { int size = intervals.size(); sort(intervals.begin(), intervals.end(), [](const vector<int>& a, const vector<int>& b) { if (a[1] == b[1]) return a[0] > b[0]; else return a[1] < b[1]; }); int ans = 0, p1 = -1, p2 = -1; for (int i = 0; i < size; ++i) { if (intervals[i][0] <= p1) continue; if (intervals[i][0] > p2) { ans += 2; p2 = intervals[i][1]; p1 = p2 - 1; } else { ans++; p1 = p2; p2 = intervals[i][1]; } } return ans; } };