timeNeededToBuyTckts.js

/* 
Time Needed to Buy Tickets
There are n people in a line queuing to buy tickets, where the 0th person is at the front of the line and the 
(n - 1)th person is at the back of the line. You are given a 0-indexed integer array tickets of length n where 
the number of tickets that the ith person would like to buy is tickets[i]. Each person takes exactly 1 second 
to buy a ticket. A person can only buy 1 ticket at a time and has to go back to the end of the line 
(which happens instantaneously) in order to buy more tickets. If a person does not have any tickets left to buy, 
the person will leave the line. Return the time taken for the person at position k (0-indexed) to finish buying tickets.

Example 1:
Input: tickets = [2,3,2], k = 2
Output: 6
Explanation: 
- In the first pass, everyone in the line buys a ticket and the line becomes [1, 2, 1].
- In the second pass, everyone in the line buys a ticket and the line becomes [0, 1, 0].
The person at position 2 has successfully bought 2 tickets and it took 3 + 3 = 6 seconds.

Example 2:
Input: tickets = [5,1,1,1], k = 0
Output: 8
Explanation:
- In the first pass, everyone in the line buys a ticket and the line becomes [4, 0, 0, 0].
- In the next 4 passes, only the person in position 0 is buying tickets.
The person at position 0 has successfully bought 5 tickets and it took 4 + 1 + 1 + 1 + 1 = 8 seconds.
*/

// O(n^2)
// var timeRequiredToBuy = function(tickets, k) {
//     let totalTime = 0
//     while(tickets[k] !== 0) {
//         tickets = tickets.map(t => {
//             if(t !== 0) totalTime += 1
//             return t > 1 ? t - 1 : 0
//         })
//     }
//     return totalTime
// };


//O(n)
var timeRequiredToBuy = function(tickets, k) {
    let totalTime = 0
    for(let i = 0; i < tickets.length; i++) {
        if(i <= k) {
            totalTime += Math.min(tickets[i], tickets[k])
        } else {
            totalTime += Math.min(tickets[i], tickets[k] - 1)
        }
    }
    return totalTime
};

console.log(timeRequiredToBuy([2,3,2], 2))
console.log(timeRequiredToBuy([5,1,1,1], 0))
console.log(timeRequiredToBuy([84,49,5,24,70,77,87,8], 3)) // 24 + 24 + 5 + 24 + 23 + 23 + 23 + 8