哈希表相关题集

剑指 Offer II 016. 不含重复字符的最长子字符串

class Solution {
    public static int lengthOfLongestSubstring(String s) {
        HashMap<Character,Integer> hashMap = new HashMap<> ();
        int max = 0;
        int left = 0;
        for(int i = 0;i < s.length();i++) {
            if(hashMap.containsKey(s.charAt(i))) {
                left = Math.max(left,hashMap.get(s.charAt(i)) + 1);
            }
            hashMap.put(s.charAt(i),i);
            max = Math.max(max,i - left + 1);
        }
        return max;
    }
}

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468. 验证IP地址

class Solution {
    public String validIPAddress(String queryIP) {
        return isIPv4(queryIP) ? "IPv4" : isIPv6(queryIP) ? "IPv6" : "Neither";
    }
    public boolean isIPv4(String s) {
        String t[] = s.split("\\.", -1);
        if(t.length != 4) {
            return false;
        }
        for(int i = 0;i < 4;i++) {
            if(t[i].length() == 0 || t[i].length() > 3 || t[i].length() > 1 && t[i].charAt(0) == '0') {
                return false;
            }
            int sum = 0;
            for(char c : t[i].toCharArray()) {
                if(!Character.isDigit(c)) {
                    return false;
                }
                sum = sum * 10 + c -'0';
            }
            if(sum > 255) {
                return false;
            }
        }
            return true;
        }
        public boolean isIPv6(String s) {
            s = s.toLowerCase();
        String t[] = s.split(":", -1);
        if(t.length != 8) {
            return false;
        }
        for(int i = 0;i < 8;i++) {
            if(t[i].length() == 0 || t[i].length() > 4) {
                return false;
            }
            for(char c : t[i].toCharArray()) {
                if(!(c >= '0' && c <= '9') && !(c >= 'a' && c <= 'f')) {
                    return false;
                }
            }
        }
        return true;
        }
}

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705. 设计哈希集合

class MyHashSet {
    private static final int BASE = 769;
    private LinkedList[] data;

    public MyHashSet() {
        data = new LinkedList[BASE];
        for (int i = 0; i < BASE; ++i) {
            data[i] = new LinkedList<Integer>();
        }
    }
    
    public void add(int key) {
        int h = hash(key);
        Iterator<Integer> iterator = data[h].iterator();
        while (iterator.hasNext()) {
            Integer element = iterator.next();
            if (element == key) {
                return;
            }
        }
        data[h].offerLast(key);
    }
    
    public void remove(int key) {
        int h = hash(key);
        Iterator<Integer> iterator = data[h].iterator();
        while (iterator.hasNext()) {
            Integer element = iterator.next();
            if (element == key) {
                data[h].remove(element);
                return;
            }
        }
    }
    
    public boolean contains(int key) {
        int h = hash(key);
        Iterator<Integer> iterator = data[h].iterator();
        while (iterator.hasNext()) {
            Integer element = iterator.next();
            if (element == key) {
                return true;
            }
        }
        return false;
    }

    private static int hash(int key) {
        return key % BASE;
    }
}

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706. 设计哈希映射

class MyHashMap {
    private class Pair {
        private int key;
        private int value;

        public Pair(int key,int value) {
            this.key = key;
            this.value = value;
        }

        public int getKey() {
            return key;
        }

        public int getValue() {
            return value;
        }

        public void setValue(int value) {
            this.value = value;
        }
    }

    public static final int BASE = 769;
    private LinkedList[] data;


    public MyHashMap() {
        data = new LinkedList[BASE];
        for(int i = 0;i < BASE; ++i) {
            data[i] = new LinkedList<Pair> ();
        }
    }
    
    public void put(int key, int value) {
        int h = hash(key);
        Iterator<Pair> iterator = data[h].iterator();
        while(iterator.hasNext()) {
            Pair pair = iterator.next();
            if(pair.getKey() == key) {
                pair.setValue(value);
                return;
            }
        }
        data[h].offerLast(new Pair(key,value));

    }
    
    public int get(int key) {
        int h = hash(key);
        Iterator<Pair> iterator = data[h].iterator();
        while(iterator.hasNext()) {
            Pair pair = iterator.next();
            if(pair.getKey() == key) {
                return pair.value;
            }
        }
        return -1;
    }
    
    public void remove(int key) {
        int h = hash(key);
        Iterator<Pair> iterator = data[h].iterator();
        while(iterator.hasNext()) {
            Pair pair = iterator.next();
            if(pair.getKey() == key) {
                data[h].remove(pair);
                return;
            }
        }
    }
    private static int hash(int key) {
        return key % BASE;
    }
}

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