Merge pull request #4 from rvguradiya/add-ecommerce_order_log_data_structure

Add solution for recording and retrieving last N order IDs using a ci…

Author: umathomprakash09

problems/queue/ecommerce_order_log_problem.md

@@ -0,0 +1,8 @@
+This problem was asked by **Twitter**.
+
+You run an e-commerce website and want to record the last N order ids in a log. Implement a data structure to accomplish this, with the following API:
+
+- record(order_id): adds the order_id to the log
+- get_last(i): gets the ith last element from the log. i is guaranteed to be smaller than or equal to N.
+
+You should be as efficient with time and space as possible.

solutions/queue/ecommerce_order_log_problem/Approach.java

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+class Approach {
+    int[] log;
+    int capacity;
+    int front;
+    int rare;
+
+    Approach(int capacity) {
+        this.capacity = capacity;
+        this.log = new int[this.capacity];
+        this.front = 0;
+        this.rare = -1;
+    }
+
+    public void record(int order_id) {
+        if (this.log.length < this.capacity) {
+            this.log[rare] = order_id;
+            this.rare++;
+        } else {
+            this.rare = (this.rare + 1) % this.capacity;
+            this.front = (this.front + 1) % this.capacity;
+            this.log[this.rare] = order_id;
+        }
+    }
+
+    public int get_last(int index) {
+        return this.log[(this.front + index - 1) % this.capacity];
+    }
+
+    public static void main(String[] args) {
+        Approach r = new Approach(5);
+        r.record(102);
+        r.record(103);
+        r.record(104);
+        r.record(105);
+        r.record(106);
+        r.record(107);
+
+        System.out.println(r.get_last(3));
+    }
+}

solutions/queue/ecommerce_order_log_problem/approach.js

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+class Record {
+  constructor(N) {
+    this.capacity = N;
+    this.log = [];
+    this.front = 0;
+    this.rare = 0;
+  }
+
+  record(order_id) {
+    if (this.log.length < this.capacity) {
+      this.log.push(order_id);
+      this.rare++;
+    } else {
+      this.rare = (this.rare + 1) % this.capacity;
+      this.front = (this.front + 1) % this.capacity;
+      this.log[this.rare] = order_id;
+    }
+  }
+
+  get_last(index) {
+    return this.log[(this.front + index - 1) % this.capacity];
+  }
+}
+
+r = new Record(5);
+r.record(102);
+r.record(103);
+r.record(104);
+r.record(105);
+r.record(106);
+r.record(107);
+
+console.log(r.get_last(3));

solutions/queue/ecommerce_order_log_problem/approach.py

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+class Record:
+    def __init__(self,N) -> None:
+        self.log = []
+        self.capacity = N
+
+    def record(self,order_id):
+        if len(self.log) < self.capacity:
+            self.log.append(order_id)
+        else:
+            self.log.pop(0)
+            self.log.append(order_id)
+    
+    def get_last(self,index):
+        return self.log[-index]
+    
+r = Record(5)
+r.record(102)
+r.record(103)
+r.record(104)
+r.record(105)
+r.record(106)
+r.record(107)
+
+print(r.get_last(3))