Create snapshot-array.cpp

Author: kamyu104

C++/snapshot-array.cpp

@@ -0,0 +1,41 @@
+// Time:  set: O(1)
+//        get: O(logn), n is the total number of set
+// Space: O(n)
+
+class SnapshotArray {
+public:
+    SnapshotArray(int length) {
+    }
+    
+    void set(int index, int val) {
+        if (!A_.count(index)) {
+            A_[index].emplace_back(-1, 0);
+        }
+        A_[index].emplace_back(snap_id_, val);
+    }
+    
+    int snap() {
+        return snap_id_++;
+    }
+    
+    int get(int index, int snap_id) {
+        if (!A_.count(index)) {
+            A_[index].emplace_back(-1, 0);
+        }
+        const auto& it = prev(upper_bound(A_[index].cbegin(), A_[index].cend(),
+                                          make_pair(snap_id + 1, 0)));
+        return it->second;
+    }
+
+private:
+    unordered_map<int, vector<pair<int, int>>> A_;
+    int snap_id_ = 0;
+};
+
+/**
+ * Your SnapshotArray object will be instantiated and called as such:
+ * SnapshotArray* obj = new SnapshotArray(length);
+ * obj->set(index,val);
+ * int param_2 = obj->snap();
+ * int param_3 = obj->get(index,snap_id);
+ */