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  • [LC] 706. Design HashMap

    Design a HashMap without using any built-in hash table libraries.

    To be specific, your design should include these functions:

    • put(key, value) : Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.
    • get(key): Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
    • remove(key) : Remove the mapping for the value key if this map contains the mapping for the key.


    Example:

    MyHashMap hashMap = new MyHashMap();
    hashMap.put(1, 1);          
    hashMap.put(2, 2);         
    hashMap.get(1);            // returns 1
    hashMap.get(3);            // returns -1 (not found)
    hashMap.put(2, 1);          // update the existing value
    hashMap.get(2);            // returns 1 
    hashMap.remove(2);          // remove the mapping for 2
    hashMap.get(2);            // returns -1 (not found) 
    
    class MyHashMap {
        private int SIZE = 1000000;
        private ListNode[] nodes;
    
        /** Initialize your data structure here. */
        public MyHashMap() {
            nodes = new ListNode[SIZE];
        }
        
        /** value will always be non-negative. */
        public void put(int key, int value) {
            int index = getIndex(key);
            if (nodes[index] == null) {
                nodes[index] = new ListNode(-1, -1);
            }
            ListNode prev = findNext(nodes[index], key);
            if (prev.next == null) {
                prev.next = new ListNode(key, value);
            } else {
                prev.next.val = value;
            }
        }
        
        /** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
        public int get(int key) {
            int index = getIndex(key);
            if (nodes[index] == null) {
                return -1;
            }
            ListNode prev = findNext(nodes[index], key);
            if (prev.next == null) {
                return -1;
            }
            return prev.next.val;
        }
        
        /** Removes the mapping of the specified value key if this map contains a mapping for the key */
        public void remove(int key) {
            int index = getIndex(key);
            if (nodes[index] == null) {
                return;
            }
            ListNode prev = findNext(nodes[index], key);
            if (prev.next == null) {
                return;
            }
            prev.next = prev.next.next;
        }
        
        private int getIndex(int key) {
            return Integer.hashCode(key) % SIZE;
        }
        
        private ListNode findNext(ListNode cur, int key) {
            while (cur.next != null && cur.next.key != key) {
                cur = cur.next;
            }
            return cur;
        }
    }
    
    class ListNode {
        int key;
        int val;
        ListNode next;
        public ListNode(int key, int val) {
            this.key = key;
            this.val = val;
        }
    }
    
    /**
     * 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);
     */
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  • 原文地址:https://www.cnblogs.com/xuanlu/p/12708635.html
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