You are driving a vehicle that has capacity empty seats initially available for passengers.  The vehicle only drives east (ie. it cannot turn around and drive west.)
Given a list of trips, trip[i] = [num_passengers, start_location, end_location] contains information about the i-th trip: the number of passengers that must be picked up, and the locations to pick them up and drop them off.  The locations are given as the number of kilometers due east from your vehicle's initial location.
Return true if and only if it is possible to pick up and drop off all passengers for all the given trips. 
Example 1:
Input: trips = [[2,1,5],[3,3,7]], capacity = 4
Output: false
Example 2:
Input: trips = [[2,1,5],[3,3,7]], capacity = 5
Output: true
Example 3:
Input: trips = [[2,1,5],[3,5,7]], capacity = 3
Output: true
Example 4:
Input: trips = [[3,2,7],[3,7,9],[8,3,9]], capacity = 11
Output: true
Constraints:
trips.length <= 1000
trips[i].length == 3
1 <= trips[i][0] <= 100
0 <= trips[i][1] < trips[i][2] <= 1000
1 <= capacity <= 100000
class Solution:
    def carPooling(self, trips: List[List[int]], capacity: int) -> bool:
        if len(trips) <=0:
            return False
        
        trips.sort(key = lambda x : x[1]) # Sorting array by start time
        stack = [] # maintaing list to store indexes so that we can compare start time of previous and with current end time
        if trips[0][0] > capacity:
            return False
        else:
            stack.append(0)
            capacity-=trips[0][0]
            
        for i in range(1, len(trips)):
            n = 0
            # if current start time >= any one of previous indices start time--> inc capacity
            while stack and n < len(stack): 
                if trips[i][1] >= trips[stack[n]][2]:
                    capacity += trips[stack[n]][0]
                    stack.pop(n)
                else: n+=1
                
            if trips[i][0] <= capacity:
                capacity-=trips[i][0]
            elif trips[i][0] > capacity:
                return False
            stack.append(i)
        return True

class Solution:
    def carPooling(self, trips: List[List[int]], capacity: int) -> bool:
        if len(trips) <=0:
            return False
        
        trips.sort(key = lambda x : x[1]) # Sorting array by start time
        stack = [] # maintaing list to store indexes so that we can compare start time of previous and with current end time
        if trips[0][0] > capacity:
            return False
        else:
            stack.append(0)
            capacity-=trips[0][0]
            
        for i in range(1, len(trips)):
            n = 0
            # if current start time >= any one of previous indices start time--> inc capacity
            while stack and n < len(stack): 
                if trips[i][1] >= trips[stack[n]][2]:
                    capacity += trips[stack[n]][0]
                    stack.pop(n)
                else: n+=1
                
            if trips[i][0] <= capacity:
                capacity-=trips[i][0]
            elif trips[i][0] > capacity:
                return False
            stack.append(i)
        return True
