Merge pull request #2534 from tonngw/main

Create: 0706-design-hashmap.cpp and 0034-find-first-and-last-position-of-element-in-sorted-array.cpp

Author: a93a

cpp/0034-find-first-and-last-position-of-element-in-sorted-array.cpp

@@ -0,0 +1,32 @@
+/*
+    Given an array of integers nums sorted in non-decreasing order, find the starting and ending position of a given target value.
+    Ex. nums = [5,7,7,8,8,10], target = 8 -> [3, 4] (start position is 3, end position is 4)
+
+    Use binary search, firstly binary search left endpoint, then binary search right endpoint.
+
+    Time: O(log n)
+    Space: O(1)
+*/
+
+class Solution {
+public:
+    vector<int> searchRange(vector<int>& nums, int target) {
+        if (nums.empty()) return {-1, -1};
+        int l = 0, r = nums.size() - 1;
+        while (l < r) {
+            int mid = l + r >> 1;
+            if (nums[mid] >= target) r = mid;
+            else l = mid + 1;
+        }
+        if (nums[l] != target) return {-1, -1};
+        int left = l;
+
+        l = 0, r = nums.size() - 1;
+        while (l < r) {
+            int mid = l + r + 1ll >> 1;
+            if (nums[mid] <= target) l = mid;
+            else r = mid - 1;
+        }
+        return {left, r};
+    }
+};

cpp/0706-design-hashmap.cpp

@@ -0,0 +1,59 @@
+/*
+    Design a HashMap without using any built-in hash table libraries.
+
+    Designing a hash table using the chaining method, where a vector holds a list of pairs representing the key-value mappings.
+
+    Time: O(n)
+    Space: O(n)
+*/
+
+class MyHashMap {
+public:
+    const int N = 10010;
+    vector<list<pair<int, int>>> h; 
+
+    /** Initialize your data structure here. */
+    MyHashMap() {
+        h = vector<list<pair<int, int>>>(N);
+    }
+    
+    list<pair<int, int>>::iterator find(int key) {
+        int t = key % N;
+        for (auto it = h[t].begin(); it != h[t].end(); it ++ ) {
+            if (it->first == key)
+                return it;
+        }
+        return h[t].end();
+    }
+
+    /** value will always be non-negative. */
+    void put(int key, int value) {
+        auto t = key % N;
+        auto it = find(key);
+        if (it == h[t].end()) h[t].push_back({key, value});
+        else it->second = value;
+    }
+    
+    /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
+    int get(int key) {
+        auto t = key % N;
+        auto it = find(key);
+        if (it != h[t].end()) return it->second;
+        return -1;
+    }
+    
+    /** Removes the mapping of the specified value key if this map contains a mapping for the key */
+    void remove(int key) {
+        auto t = key % N;
+        auto it = find(key);
+        if (it != h[t].end()) h[t].erase(it);
+    }
+};
+
+/**
+ * Your MyHashMap object will be instantiated and called as such:
+ * MyHashMap* obj = new MyHashMap();
+ * obj->put(key,value);
+ * int param_2 = obj->get(key);
+ * obj->remove(key);
+ */