Problem

You are given a string s. Simulate events at each second i:

If s[i] == ‘E’, a person enters the waiting room and takes one of the chairs in it. If s[i] == ‘L’, a person leaves the waiting room, freeing up a chair.

Return the minimum number of chairs needed so that a chair is available for every person who enters the waiting room given that it is initially empty.

Example 1:

Input: s = “EEEEEEE”

Output: 7

Explanation:

After each second, a person enters the waiting room and no person leaves it. Therefore, a minimum of 7 chairs is needed.

Example 2:

Input: s = “ELELEEL”

Output: 2

Explanation:

Let’s consider that there are 2 chairs in the waiting room. The table below shows the state of the waiting room at each second.

Second Event People in the Waiting Room Available Chairs 0 Enter 1 1 1 Leave 0 2 2 Enter 1 1 3 Leave 0 2 4 Enter 1 1 5 Enter 2 0 6 Leave 1 1

Example 3:

Input: s = “ELEELEELLL”

Output: 3

Explanation:

Let’s consider that there are 3 chairs in the waiting room. The table below shows the state of the waiting room at each second.

Second Event People in the Waiting Room Available Chairs 0 Enter 1 2 1 Leave 0 3 2 Enter 1 2 3 Enter 2 1 4 Leave 1 2 5 Enter 2 1 6 Enter 3 0 7 Leave 2 1 8 Leave 1 2 9 Leave 0 3

Constraints:

1 <= s.length <= 50 s consists only of the letters ‘E’ and ‘L’. s represents a valid sequence of entries and exits.

Pre analysis

This is a simple problem where we need to keep track of number of chairs needed at each second. We can keep track of number of chairs needed at each second and return the maximum number of chairs needed.