LeetCode //C - 933. Number of Recent Calls

933. Number of Recent Calls

You have a RecentCounter class which counts the number of recent requests within a certain time frame.

Implement the RecentCounter class:

• RecentCounter() Initializes the counter with zero recent requests.
• int ping(int t) Adds a new request at time t, where t represents some time in milliseconds, and returns the number of requests that has happened in the past 3000 milliseconds (including the new request). Specifically, return the number of requests that have happened in the inclusive range [t - 3000, t].

It is guaranteed that every call to ping uses a strictly larger value of t than the previous call.
 

Example 1:

Input
[“RecentCounter”, “ping”, “ping”, “ping”, “ping”]
[[], [1], [100], [3001], [3002]]
Output
[null, 1, 2, 3, 3]
Explanation
RecentCounter recentCounter = new RecentCounter();
recentCounter.ping(1); // requests = [1], range is [-2999,1], return 1
recentCounter.ping(100); // requests = [1, 100], range is [-2900,100], return 2
recentCounter.ping(3001); // requests = [1, 100, 3001], range is [1,3001], return 3
recentCounter.ping(3002); // requests = [1, 100, 3001, 3002], range is [2,3002], return 3

Constraints:

• $1<=t<=10^9$
• Each test case will call ping with strictly increasing values of t.
• At most $10^4$ calls will be made to ping.

From: LeetCode
Link: 933. Number of Recent Calls

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Solution:

Ideas：

• The RecentCounter is essentially maintaining a dynamic list of timestamps representing request times.
• When a new request comes in (signified by calling recentCounterPing with a timestamp), it’s added to this list.
• The recentCounterPing function then counts how many of these stored requests fall within the last 3000 milliseconds (inclusive of the new request).
• This count is returned as the number of recent requests.

Code:

typedef struct {
    int *requests;    // Array to store the timestamps of requests
    int size;         // Current number of requests stored
    int capacity;     // Total capacity of the array
} RecentCounter;

RecentCounter* recentCounterCreate() {
    RecentCounter* obj = (RecentCounter*) malloc(sizeof(RecentCounter));
    obj->capacity = 10; // Initial capacity
    obj->size = 0;
    obj->requests = (int*) malloc(obj->capacity * sizeof(int));
    return obj;
}

// Helper function to resize the array if needed
void resizeIfNeeded(RecentCounter* obj) {
    if (obj->size >= obj->capacity) {
        obj->capacity *= 2;
        obj->requests = (int*) realloc(obj->requests, obj->capacity * sizeof(int));
    }
}

int recentCounterPing(RecentCounter* obj, int t) {
    // Resize the array if needed
    resizeIfNeeded(obj);

    // Add the new request
    obj->requests[obj->size++] = t;

    // Calculate the minimum acceptable time
    int minTime = t - 3000;

    // Count requests within the time frame
    int count = 0;
    for (int i = 0; i < obj->size; ++i) {
        if (obj->requests[i] >= minTime) {
            ++count;
        }
    }

    return count;
}

void recentCounterFree(RecentCounter* obj) {
    free(obj->requests);
    free(obj);
}

/**
 * Your RecentCounter struct will be instantiated and called as such:
 * RecentCounter* obj = recentCounterCreate();
 * int param_1 = recentCounterPing(obj, t);
 * recentCounterFree(obj);
 */