fixed: several bugs

docs/chapter_hashing/hash_map.md

@@ -510,7 +510,7 @@ $$
 === "TypeScript"
 
     ```typescript title="array_hash_map.ts"
-    /* 键值对 int->String */
+    /* 键值对 Number -> String */
     class Entry {
         public key: number;
         public val: string;
@@ -538,19 +538,23 @@ $$
         public set(key: number, val: string | null) {
             if (val !== null) {
                 this.elements[key] = new Entry(key, val);
+            } else {
+                this.elements[key] = null as any;
             }
-            this.elements[key] = null as any;
         }
         
         /* 获取 */
-        public get(key: number): string {
-            return this.elements[key].val;
+        public get(key: number): string | null {
+            if (this.elements[key] instanceof Entry) {
+                return this.elements[key].val;
+            }
+            return null;
         }
         
         public entrySet() {
-            let arr = [];
+        let arr = [];
             for (let i = 0; i < this.elements.length; i++) {
-                if (this.elements[i] !== null) {
+                if (this.elements[i]) {
                     arr.push(this.elements[i]);
                 }
             }
@@ -560,7 +564,7 @@ $$
         public valueSet() {
             let arr = [];
             for (let i = 0; i < this.elements.length; i++) {
-                if (this.elements[i] !== null) {
+                if (this.elements[i]) {
                     arr.push(this.elements[i].val);
                 }
             }
@@ -570,13 +574,64 @@ $$
         public keySet() {
             let arr = [];
             for (let i = 0; i < this.elements.length; i++) {
-                if (this.elements[i] !== null) {
+                if (this.elements[i]) {
                     arr.push(this.elements[i].key);
                 }
             }
             return arr;
         }
     }
+
+    /* 基于数组简易实现的哈希表 */
+    class ArrayHashMap {
+        // 初始化一个长度为 100 的桶（数组）
+        private bucket: ArrayList;
+    
+        constructor() {
+            this.bucket = new ArrayList(100);
+        }
+    
+        /* 哈希函数 */
+        private hashFunc(key: number): number {
+            return key % 100;
+        }
+    
+        /* 查询操作 */
+        public get(key: number): string | null {
+            let index = this.hashFunc(key);
+            let val = this.bucket.get(index);
+            if (val === null) return null;
+            return val;
+        }
+    
+        /* 添加操作 */
+        public put(key: number, val: string) {
+            let index = this.hashFunc(key);
+            this.bucket.set(index, val);
+        }
+    
+        /* 删除操作 */
+        public remove(key: number) {
+            let index = this.hashFunc(key);
+            // 置为 null ，代表删除
+            this.bucket.set(index, null);
+        }
+    
+        /* 获取所有键值对 */
+        public entrySet(): Entry[] {
+            return this.bucket.entrySet();
+        }
+    
+        /* 获取所有键 */
+        public keySet(): number[] {
+            return this.bucket.keySet();
+        }
+    
+        /* 获取所有值 */
+        public valueSet(): string[] {
+            return this.bucket.valueSet();
+        }
+    }
     ```
 
 === "C"