706. Design HashMap: AC

Author: tan-wei

src/solution/mod.rs

@@ -514,3 +514,4 @@ mod s0701_insert_into_a_binary_search_tree;
 mod s0703_kth_largest_element_in_a_stream;
 mod s0704_binary_search;
 mod s0705_design_hashset;
+mod s0706_design_hashmap;

src/solution/s0706_design_hashmap.rs

@@ -0,0 +1,113 @@
+/**
+ * [0706] Design HashMap
+ *
+ * Design a HashMap without using any built-in hash table libraries.
+ * Implement the MyHashMap class:
+ *
+ * 	MyHashMap() initializes the object with an empty map.
+ * 	void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
+ * 	int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
+ * 	void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.
+ *
+ *  
+ * Example 1:
+ *
+ * Input
+ * ["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
+ * [[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
+ * Output
+ * [null, null, null, 1, -1, null, 1, null, -1]
+ * Explanation
+ * MyHashMap myHashMap = new MyHashMap();
+ * myHashMap.put(1, 1); // The map is now [[1,1]]
+ * myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
+ * myHashMap.get(1);    // return 1, The map is now [[1,1], [2,2]]
+ * myHashMap.get(3);    // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
+ * myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
+ * myHashMap.get(2);    // return 1, The map is now [[1,1], [2,1]]
+ * myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
+ * myHashMap.get(2);    // return -1 (i.e., not found), The map is now [[1,1]]
+ *
+ *  
+ * Constraints:
+ *
+ * 	0 <= key, value <= 10^6
+ * 	At most 10^4 calls will be made to put, get, and remove.
+ *
+ */
+pub struct Solution {}
+
+// problem: https://leetcode.com/problems/design-hashmap/
+// discuss: https://leetcode.com/problems/design-hashmap/discuss/?currentPage=1&orderBy=most_votes&query=
+
+// submission codes start here
+
+const TABLE_SIZE: usize = 32;
+
+#[derive(Default)]
+struct MyHashMap {
+    table: [Vec<(i32, i32)>; TABLE_SIZE],
+}
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl MyHashMap {
+    fn new() -> Self {
+        Default::default()
+    }
+
+    fn put(&mut self, key: i32, value: i32) {
+        let i = (key as usize) % TABLE_SIZE;
+        if let Some(j) = self.table[i].iter().position(|&(k, _)| k == key) {
+            self.table[i][j].1 = value;
+        } else {
+            self.table[i].push((key, value));
+        }
+    }
+
+    fn get(&mut self, key: i32) -> i32 {
+        let i = (key as usize) % TABLE_SIZE;
+        self.table[i]
+            .iter()
+            .position(|&(k, _)| k == key)
+            .map(|j| self.table[i][j].1)
+            .unwrap_or(-1)
+    }
+
+    fn remove(&mut self, key: i32) {
+        let i = (key as usize) % TABLE_SIZE;
+        if let Some(j) = self.table[i].iter().position(|&(k, _)| k == key) {
+            self.table[i].remove(j);
+        }
+    }
+}
+
+/**
+ * Your MyHashMap object will be instantiated and called as such:
+ * let obj = MyHashMap::new();
+ * obj.put(key, value);
+ * let ret_2: i32 = obj.get(key);
+ * obj.remove(key);
+ */
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_0706_example_1() {
+        let mut my_hash_map = MyHashMap::new();
+        my_hash_map.put(1, 1); // The map is now [[1,1]]
+        my_hash_map.put(2, 2); // The map is now [[1,1], [2,2]]
+        assert_eq!(my_hash_map.get(1), 1); // return 1, The map is now [[1,1], [2,2]]
+        assert_eq!(my_hash_map.get(3), -1); // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
+        my_hash_map.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
+        assert_eq!(my_hash_map.get(2), 1); // return 1, The map is now [[1,1], [2,1]]
+        my_hash_map.remove(2); // remove the mapping for 2, The map is now [[1,1]]
+        assert_eq!(my_hash_map.get(2), -1); // return -1 (i.e., not found), The map is now [[1,1]]
+    }
+}