# Count maximum number of cars parked at the same time

• Difficulty Level : Medium
• Last Updated : 23 Aug, 2021

Given a 2d array arr[][] with each row representing a pair representing entry and exit time of a car in a parking lot, the task is to calculate the maximum number of cars that can be parked at the same time.

Examples:

Input: arr[][] = {{1012, 1136}, {1317, 1417}, {1015, 1020}}
Output: 2
Explanation:
1st car entered at 10:12 and exits at 11:36 and 3rd car entered at 10:15 and exits at 10:20.
Therefore, 1st and 3rd car are present at the same time.

Input: arr[][] = {{1120, 1159}, {1508, 1529}, {1508, 1527}, {1503, 1600}, {1458, 1629}, {1224, 1313}}
Output: 4
Explanation: 2nd, 3rd, 4th and 5th cars are present at the same time.

Approach: The idea is to use Kadane’s algorithm to solve this problem. Follow the steps below to solve the problem:

• Initialize a vector of pairs to store the entry or exit time as the first element of a pair and true as the second element of a pair, if corresponding time stored is entry time. Otherwise, store as false.
• Sort the vector in non-decreasing order of time.
• Initialize two variables, say curMax, to look for all true contiguous segments of the array, and maxFinal, to keep track of longest true contiguous segment among all true segments.
• Iterate over the range [0, 2*N – 1]:
• If a car entered, increment curMax by 1.
• Otherwise:
• If curMax > maxFinal, update maxFinal = curMax.
• Whenever a car exits, subtract curMax by 1.
• Print maxFinal as the answer.

Below is the implementation of the above approach:

## C++

 // C++ program for the above approach #include using namespace std; // Function to count maximum number// of cars parked at the sameint maxCars(int arr[][2], int N){    // Stores info about    // entry and exit times    pair a[2 * N];     // Convert given array to new array    for (int i = 0; i < N; i++) {        a[2 * i] = { arr[i][0], true };        a[2 * i + 1] = { arr[i][1], false };    }     // Sort array in ascending    // order of time    sort(a, a + 2 * N);     // Stores current maximum    // at every iteration    int curMax = 0;     // Stores final maximum number    // of cars parked at any time    int maxFinal = 0;     // Traverse the array    for (int i = 0; i < 2 * N; ++i) {         // When car entered        if (a[i].second) {            curMax++;        }         // When car exits        else {            if (curMax > maxFinal) {                maxFinal = curMax;            }            curMax--;        }    }     // Print the answer    cout << maxFinal;} // Driver Codeint main(){    // Given array    int arr[][2] = { { 1012, 1136 },                     { 1317, 1412 },                     { 1015, 1020 } };     // Size of the array    int N = sizeof(arr) / sizeof(arr[0]);     // Function Call    maxCars(arr, N);     return 0;}

## Java

 // Java program for the above approachimport java.io.*;import java.lang.*;import java.util.*; class GFG{ // Pair classstatic class pair{    int first;    boolean second;     pair(int first, boolean second)    {        this.first = first;        this.second = second;    }} // Function to count maximum number// of cars parked at the samestatic void maxCars(int arr[][], int N){         // Stores info about    // entry and exit times    pair a[] = new pair[2 * N];     // Convert given array to new array    for(int i = 0; i < N; i++)    {        a[2 * i] = new pair(arr[i][0], true);        a[2 * i + 1] = new pair(arr[i][1], false);    }     // Sort array in ascending    // order of time    Arrays.sort(a, (p1, p2) -> p1.first - p2.first);     // Stores current maximum    // at every iteration    int curMax = 0;     // Stores final maximum number    // of cars parked at any time    int maxFinal = 0;     // Traverse the array    for(int i = 0; i < 2 * N; ++i)    {                 // When car entered        if (a[i].second)        {            curMax++;        }         // When car exits        else        {            if (curMax > maxFinal)            {                maxFinal = curMax;            }            curMax--;        }    }     // Print the answer    System.out.println(maxFinal);} // Driver Codepublic static void main(String[] args){         // Given array    int arr[][] = { { 1012, 1136 },                    { 1317, 1412 },                    { 1015, 1020 } };     // Size of the array    int N = arr.length;     // Function Call    maxCars(arr, N);}} // This code is contributed by Kingash

## Python3

 # Python3 program for the above approach # Function to count maximum number# of cars parked at the samedef maxCars(arr, N):       # Stores info about    # entry and exit times    a = [[0,True] for i in range(2 * N)]     # Convert given array to new array    for i in range(N):        a[2 * i] = [arr[i][0], True]        a[2 * i + 1] = [arr[i][1], False]     # Sort array in ascending    # order of time    a = sorted(a)     # Stores current maximum    # at every iteration    curMax = 0     # Stores final maximum number    # of cars parked at any time    maxFinal = 0     # Traverse the array    for i in range(2*N):         # When car entered        if (a[i][1]):            curMax += 1        # When car exits        else:            if (curMax > maxFinal):                maxFinal = curMax            curMax -= 1     # Print answer    print (maxFinal) # Driver Codeif __name__ == '__main__':    # Given array    arr= [ [ 1012, 1136 ],         [ 1317, 1412 ],         [ 1015, 1020 ]]     # Size of the array    N = len(arr)     # Function Call    maxCars(arr, N) # This code is contributed by mohit kumar 29.

## C#

 // C# program for the above approachusing System;class GFG{    // Function to count maximum number    // of cars parked at the same    static void maxCars(int[,] arr, int N)    {               // Stores info about        // entry and exit times        Tuple[] a = new Tuple[2 * N];              // Convert given array to new array        for (int i = 0; i < N; i++) {            a[2 * i] = new Tuple(arr[i,0], true);            a[2 * i + 1] = new Tuple(arr[i,1], false);        }              // Stores current maximum        // at every iteration        int curMax = 1;              // Stores final maximum number        // of cars parked at any time        int maxFinal = 0;              // Traverse the array        for (int i = 0; i < 2 * N; ++i) {                  // When car entered            if (a[i].Item2) {                curMax++;            }                  // When car exits            else {                if (curMax > maxFinal) {                    maxFinal = curMax;                }                curMax--;            }        }              // Print the answer        Console.WriteLine(maxFinal);    }   static void Main ()  {    // Given array    int[,] arr = { { 1012, 1136 },                    { 1317, 1412 },                    { 1015, 1020 } };      // Size of the array    int N = 2;      // Function Call    maxCars(arr, N);  }} // This code is contributed by suresh07.

## Javascript


Output:
2

Time Complexity: O(N)
Auxiliary Space: O(N)

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