**Rate Limiter - Amazon Top Interview Questions**

### Problem Statement :

Implement a rate limiter that limits users’ requests with the following methods: RateLimiter(int expire) constructs a new rate limiter with the given expire time. limit(int uid, int timestamp) represents a request from user uid at time timestamp and should return whether the given user’s request fails. It should fail if the user had a successful request less than expire time ago. You can assume that timestamp is monotonically increasing between requests. Constraints n ≤ 100,000 where n is the number of calls to limit. Example 1 Input methods = ["constructor", "limit", "limit", "limit", "limit"] arguments = [[5], [0, 10], [0, 15], [0, 16], [1, 17]]` Output [None, False, False, True, False] Explanation rl = RateLimiter(5) rl.limit(0, 10) == False rl.limit(0, 15) == False rl.limit(0, 16) == True rl.limit(1, 17) == False Example 2 Input methods = ["constructor", "limit", "limit", "limit", "limit"] arguments = [[0], [0, 1], [0, 1], [0, 2], [0, 3]]` Output [None, False, False, False, False] Explanation rl = RateLimiter(0) rl.limit(0, 1) == False rl.limit(0, 1) == False rl.limit(0, 2) == False rl.limit(1, 3) == False Example 3 Input methods = ["constructor", "limit", "limit", "limit"] arguments = [[5], [0, 10], [0, 13], [0, 16]]` Output [None, False, True, False] Explanation rl = RateLimiter(5) rl.limit(0, 10) == False rl.limit(0, 13) == True rl.limit(0, 16) == False

### Solution :

` ````
Solution in C++ :
class RateLimiter {
public:
RateLimiter(int expire) : limitThreshold(expire) {
} // Remember the limit value
bool limit(int uid, int timestamp) {
// If the new request came later than minimum allowed we return false and create a new
// minimum allowed request time
if (timestamp >= lastTime[uid]) {
lastTime[uid] = timestamp + limitThreshold;
return false;
}
return true; // Reject the request
}
private:
unordered_map<int, int> lastTime; // Storage of uid and minimum allowed request time
// (initialized to 0 when the first requests comes)
int limitThreshold; // Limit value
};
```

` ````
Solution in Java :
import java.util.*;
class RateLimiter {
public int expire;
public HashMap<Integer, Integer> hm = new HashMap<>();
public RateLimiter(int expire) {
this.expire = expire;
}
public boolean limit(int uid, int timestamp) {
if (hm.containsKey(uid)) {
if (hm.get(uid) <= timestamp) {
hm.put(uid, timestamp + expire);
return false;
}
return true;
} else {
hm.put(uid, timestamp + expire);
return false;
}
}
}
```

` ````
Solution in Python :
class RateLimiter:
def __init__(self, expire):
self.expire = expire
self.lastCall = defaultdict(lambda: -1)
def limit(self, uid, timestamp):
last = self.lastCall[uid]
if last == -1 or last + self.expire <= timestamp:
self.lastCall[uid] = timestamp
return False
return True
```

## View More Similar Problems

## Self-Driving Bus

Treeland is a country with n cities and n - 1 roads. There is exactly one path between any two cities. The ruler of Treeland wants to implement a self-driving bus system and asks tree-loving Alex to plan the bus routes. Alex decides that each route must contain a subset of connected cities; a subset of cities is connected if the following two conditions are true: There is a path between ever

View Solution →## Unique Colors

You are given an unrooted tree of n nodes numbered from 1 to n . Each node i has a color, ci. Let d( i , j ) be the number of different colors in the path between node i and node j. For each node i, calculate the value of sum, defined as follows: Your task is to print the value of sumi for each node 1 <= i <= n. Input Format The first line contains a single integer, n, denoti

View Solution →## Fibonacci Numbers Tree

Shashank loves trees and math. He has a rooted tree, T , consisting of N nodes uniquely labeled with integers in the inclusive range [1 , N ]. The node labeled as 1 is the root node of tree , and each node in is associated with some positive integer value (all values are initially ). Let's define Fk as the Kth Fibonacci number. Shashank wants to perform 22 types of operations over his tree, T

View Solution →## Pair Sums

Given an array, we define its value to be the value obtained by following these instructions: Write down all pairs of numbers from this array. Compute the product of each pair. Find the sum of all the products. For example, for a given array, for a given array [7,2 ,-1 ,2 ] Note that ( 7 , 2 ) is listed twice, one for each occurrence of 2. Given an array of integers, find the largest v

View Solution →## Lazy White Falcon

White Falcon just solved the data structure problem below using heavy-light decomposition. Can you help her find a new solution that doesn't require implementing any fancy techniques? There are 2 types of query operations that can be performed on a tree: 1 u x: Assign x as the value of node u. 2 u v: Print the sum of the node values in the unique path from node u to node v. Given a tree wi

View Solution →## Ticket to Ride

Simon received the board game Ticket to Ride as a birthday present. After playing it with his friends, he decides to come up with a strategy for the game. There are n cities on the map and n - 1 road plans. Each road plan consists of the following: Two cities which can be directly connected by a road. The length of the proposed road. The entire road plan is designed in such a way that if o

View Solution →