Formatted question description: https://leetcode.ca/all/2054.html

2054. Two Best Non-Overlapping Events (Medium)

You are given a 0-indexed 2D integer array of events where events[i] = [startTimei, endTimei, valuei]. The ith event starts at startTimei and ends at endTimei, and if you attend this event, you will receive a value of valuei. You can choose at most two non-overlapping events to attend such that the sum of their values is maximized.

Return this maximum sum.

Note that the start time and end time is inclusive: that is, you cannot attend two events where one of them starts and the other ends at the same time. More specifically, if you attend an event with end time t, the next event must start at or after t + 1.

 

Example 1:

Input: events = [[1,3,2],[4,5,2],[2,4,3]]
Output: 4
Explanation: Choose the green events, 0 and 1 for a sum of 2 + 2 = 4.

Example 2:

Example 1 Diagram

Input: events = [[1,3,2],[4,5,2],[1,5,5]]
Output: 5
Explanation: Choose event 2 for a sum of 5.

Example 3:

Input: events = [[1,5,3],[1,5,1],[6,6,5]]
Output: 8
Explanation: Choose events 0 and 2 for a sum of 3 + 5 = 8.

 

Constraints:

  • 2 <= events.length <= 105
  • events[i].length == 3
  • 1 <= startTimei <= endTimei <= 109
  • 1 <= valuei <= 106

Companies:
razorpay

Related Topics:
Array, Binary Search, Dynamic Programming, Sorting, Heap (Priority Queue)

Similar Questions:

Solution 1. Mono-stack

// OJ: https://leetcode.com/problems/two-best-non-overlapping-events/
// Time: O(NlogN)
// Space: O(N)
class Solution {
public:
    int maxTwoEvents(vector<vector<int>>& A) {
        sort(begin(A), end(A));
        int N = A.size(), ans = 0, mx = 0;
        stack<pair<int, int>> s; // startTime, val
        for (int i = N - 1; i >= 0; --i) {
            if (s.empty() || s.top().second < A[i][2]) s.emplace(A[i][0], A[i][2]);
            ans = max(ans, A[i][2]);
        }
        sort(begin(A), end(A), [](auto &a, auto &b) { return a[1] < b[1]; });
        for (int i = 0; i < N && s.size(); ++i) {
            while (s.size() && s.top().first <= A[i][1]) s.pop();
            mx = max(mx, A[i][2]);
            if (s.size()) ans = max(ans, mx + s.top().second);
        }
        return ans;
    }
};
// OJ: https://leetcode.com/problems/two-best-non-overlapping-events/
// Time: O(NlogN)
// Space: O(N)
class Solution {
public:
    int maxTwoEvents(vector<vector<int>>& A) {
        sort(begin(A), end(A));
        int N = A.size(), ans = 0;
        map<int, int> m;
        for (int i = N - 1, mx = 0; i >= 0; --i) {
            m[A[i][0]] = (mx = max(mx, A[i][2]));
            ans = max(ans, A[i][2]);
        }
        sort(begin(A), end(A), [](auto &a, auto &b) { return a[1] < b[1]; });
        for (int i = 0, mx = 0; i < N; ++i) {
            mx = max(mx, A[i][2]);
            auto it = m.upper_bound(A[i][1]);
            if (it != m.end()) ans = max(ans, mx + it->second);
        }
        return ans;
    }
};
// OJ: https://leetcode.com/problems/two-best-non-overlapping-events/
// Time: O(NlogN)
// Space: O(N)
class Solution {
public:
    int maxTwoEvents(vector<vector<int>>& A) {
        sort(begin(A), end(A));
        int N = A.size(), ans = 0, mx = 0;
        map<int, int> m;  // startTime -> maxVal
        for (int i = N - 1; i >= 0; --i) {
            mx = max(mx, A[i][2]);
            auto it = m.upper_bound(A[i][1]);
            if (it != m.end()) ans = max(ans, A[i][2] + it->second);
            m[A[i][0]] = mx;
        }
        return max(ans, mx);
    }
};

Solution 4. Line Sweep

// OJ: https://leetcode.com/problems/two-best-non-overlapping-events/
// Time: O(NlogN)
// Space: O(N)
// Ref: https://leetcode.com/problems/two-best-non-overlapping-events/discuss/1552570/Very-Simple-sort-%2B-greedy%3A-No-DP-no-Binary-Search-no-HeapPQBST
class Solution {
public:
    int maxTwoEvents(vector<vector<int>>& A) {
        vector<array<int, 3>> B; // time, isStart, value
        for (auto &e : A) {
            B.push_back({ e[0], 1, e[2] });
            B.push_back({ e[1] + 1, 0, e[2] });
        }
        sort(begin(B), end(B));
        int ans = 0, maxEndValue = 0;
        for (auto &[time, isStart, value] : B) {
            if (isStart) ans = max(ans, value + maxEndValue);
            else maxEndValue = max(maxEndValue, value);
        }
        return ans;
    }
};

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