Hashtable

1. Intersection of two arrays

一个hash表存一数组，一hash表存结果

    public int[] intersection(int[] nums1, int[] nums2) {
        // Write your code here
        HashSet<Integer> set1 = new HashSet<>();
        for (int i = 0; i < nums1.length; i++)
        {
            set1.add(nums1[i]);
        }
         HashSet<Integer> set2 = new HashSet<>();
         for (int i = 0; i < nums2.length; i++)
         {
             if (set1.contains(nums2[i]) && !set2.contains(nums2[i]))
            {
                set2.add(nums2[i]);
            }
         }
         int[] res = new int[set2.size()];
         int index = 0;
         for (int i : set2)
         {
             res[index++] = i;
         }
         return res;
    }

2. Intersection of two arrays II  数的个数也算

找map记录一的个数，到2如有减去后添加到列表

    public int[] intersection(int[] nums1, int[] nums2) {
        // Write your code here
        HashMap<Integer, Integer> map1 = new HashMap<>();
        for (int i = 0; i < nums1.length; i++)
        {
            map1.put(nums1[i], map1.containsKey(nums1[i]) ? map1.get(nums1[i]) + 1: 1);
        }
        List<Integer> res = new ArrayList<>();
        for (int i = 0; i < nums2.length; i++)
        {
            if (map1.containsKey(nums2[i]) && map1.get(nums2[i]) > 0)
            {
                res.add(nums2[i]);
                map1.put(nums2[i],map1.get(nums2[i]) - 1);
            }
        }
        int[] item = new int[res.size()];
        for (int i = 0; i < res.size(); i++) {
            item[i] = res.get(i);
        }
        return item;
    }

3.Huppy Numbera

如果是，则必重复，快慢指针

    public boolean isHappy(int n) {
        // Write your code here
        if (n <= 0)
        {
            return false;
        }
        int fast = n;
        int slow = n;
        do {
            slow = calc(slow);
            fast = calc(fast);
            fast = calc(fast);
            if (fast == 1)
            {
                return true;
            }
        }while (fast != slow);
        return false;
}
    public int calc(int n)
    {
        int sum = 0;
        while (n != 0)
        {
            sum +=  (n % 10) * (n % 10);
            n /= 10;
        }
        return sum;
    }

4. Max poins on line

    public int maxPoints(Point[] points) 
   {
        if (points == null|| points.length == 0)
        {
            return 0;
        }
        int max = 1;
        double radio = 0.0;
        for (int i = 0; i < points.length - 1; i++)
        {
            int numofsame = 1;
            int localmax = 0;
            HashMap<Double, Integer> map = new HashMap<>();
            for (int j = i + 1; j < points.length; j++)
            {
                if (points[i].x == points[j].x && points[i].y == points[j].y)
                {
                    numofsame ++;
                    continue;
                } else if(points[i].x == points[j].x)
                {
                    radio = Double.MAX_VALUE;
                } else if (points[i].y == points[j].y)
                {
                    radio = 0.0;
                } else
                {
                    radio = (double)(points[i].y - points[j].y) /  (double)(points[i].x - points[j].x);
                }
                map.put(radio, map.containsKey(radio) ? map.get(radio) + 1 : 1);
            }
            for (Integer num : map.values())
            {
                if (localmax < num)
                {
                    localmax = num;
                }
            }
           localmax = localmax + numofsame;
            max = localmax > max ? localmax : max;
        }
        return max;
   }

5 Longest subString without Repeating Character

记录左右边界，最大长度，和里面的字母

    public int lengthOfLongestSubstring(String s) {  
        if(s==null || s.length()==0)  
            return 0;  
        HashSet<Character> set = new HashSet<Character>();  
        int max = 0;  
        int walker = 0;  
        int runner = 0;  
        while(runner<s.length())  
        {  
            if(set.contains(s.charAt(runner)))  
            {  
                if(max<runner-walker)  
                {  
                    max = runner-walker;  
                }  
                while(s.charAt(walker)!=s.charAt(runner))  
                {  
                    set.remove(s.charAt(walker));  
                    walker++;  
                }  
                walker++;  
            }  
            else  
            {  
                set.add(s.charAt(runner));  
            }  
            runner++;  
        }  
        max = Math.max(max,runner-walker);  
        return max;  
    } 

    public int lengthOfLongestSubstring(String s) {  
        if(s==null || s.length()==0)  
            return 0;  
       int[] res = new int[256];
       int i = 0;
       int j = 0;
       int max = 0;
       for (i = 0; i < s.length(); i++)
       {
           while (j < s.length() && res[s.charAt(j)] == 0)
           {
               max = Math.max(max, j - i + 1);
               res[s.charAt(j)] = 1;
               j++;
           }
          res[s.charAt(i)] = 0;
       }
       return max;
    }

 6 Anagrams

hashMap 记录有相同字符的 序列

    public ArrayList<String> anagrams(String[] strs) 
    {
        ArrayList<String> res = new ArrayList<String>();
        if (strs == null || strs.length == 0)
        {
            return res;
        }
        HashMap<String, ArrayList<String>> map = new HashMap<>();
        for (int i = 0; i < strs.length; i++)
        {
            char[] item = strs[i].toCharArray();
            Arrays.sort(item);
            String str = new String(item);
            if (map.containsKey(str))
            {
                ArrayList<String> list = map.get(str);
                list.add(strs[i]);
            }
            else
            {
                ArrayList<String> list = new ArrayList<String>();
                list.add(strs[i]);
                map.put(str,list);
            }
        }
        for (ArrayList<String> list: map.values())
        {
            if (list.size() > 1)
            {
                res.addAll(list);
            }
        }
        return res;
    }

7,Subarray Sum

hashMap 记录和 和坐标  找相同返回，更新hashmap

    public ArrayList<Integer> subarraySum(int[] nums) {
        // write your code here
        ArrayList<Integer> res = new ArrayList<>();
        HashMap<Integer, Integer> map = new HashMap<>();
        map.put(0, -1);
        int sum = 0;
        for (int i = 0; i < nums.length; i++)
        {
            sum += nums[i];
            if (map.containsKey(sum))
            {
                res.add(map.get(sum) + 1);
                res.add(i);
                return res;
            }
            map.put(sum, i);
        }
        return res;
    }

8, Rehashing

按照原数组遍历，如到一个不为null，继续next

    public ListNode[] rehashing(ListNode[] hashTable) {
        // write your code here
        if (hashTable == null || hashTable.length == 0)
        {
            return hashTable;
        }
        int newLen = hashTable.length * 2;
        ListNode[] newTable = new ListNode[newLen];
        for (int i = 0; i < hashTable.length; i++)
        {
            while (hashTable[i] != null)
            {
                int newIndex = (hashTable[i].val % newLen + newLen) % newLen;
                if (newTable[newIndex] == null)
                {
                    ListNode item = new ListNode(hashTable[i].val);
                    newTable[newIndex] = item;
                }else
                {
                    ListNode item = newTable[newIndex];
                    while (item.next != null)
                    {
                        item = item.next;
                    }
                    item.next = new ListNode(hashTable[i].val);
                }
                hashTable[i] = hashTable[i].next;
            }
        }
        return newTable;
    }

9.Hash Function

按哈希函数做, long 避免溢出

    public int hashCode(char[] key,int HASH_SIZE) {
        // write your code here
        long res = 0;
        for (int i = 0; i < key.length; i++)
        {
            res = (res * 33 + key[i]) %  HASH_SIZE;
        }
        return (int)res;
    }

10. Copy List with Random Pointer

一原一副，连随便，切开 切开错

    public RandomListNode copyRandomList(RandomListNode head) 
    {
        if (head == null)
        {
            return head;
        }
        RandomListNode help = head;
        while (help != null)
        {
            RandomListNode item = new RandomListNode(help.label);
            item.next = help.next;
            help.next = item;
            help = item.next;
        }
        help = head;
        while (help != null)
        {
            if (help.random != null)
            {
                help.next.random = help.random.next;
            }
            help = help.next.next;
        }
        RandomListNode newHead = head.next;
        help = head;
        while (help != null)
        {
            RandomListNode node = help.next;
            help.next = node.next;
            if (node.next != null)
            {
                node.next = node.next.next;
            }
            help = help.next;
        }
        return newHead;
    }

11.Two Sum

数组两值，hashMap 记录元素

    public int[] twoSum(int[] numbers, int target) 
    {
        if (numbers == null || numbers.length < 2)
        {
            return null;
        }
        int[] res = new int[2];
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int i = 0; i < numbers.length; i++)
        {
            if (map.containsKey(target - numbers[i]))
            {
                res[0] = map.get(target - numbers[i]) + 1;
                res[1] = i + 1;
                return res;
            }
            map.put(numbers[i], i);
        }
        return res;
    }

12. Majority Number III

建k-1hashmap ，如多删， 找到值，

    public int majorityNumber(ArrayList<Integer> nums, int k) {
        // write your code
        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int e : nums)
        {
            map.put(e, map.containsKey(e)? map.get(e)+1:1);
            if (map.size() >= k)
            {
                remove(map);
            }
        }
        if (map.size() == 0)
        {
             return Integer.MIN_VALUE;
        }
        for (int e: map.keySet())
        {
            map.put(e,0);
        }
        for (int e : nums)
        {
            if (map.containsKey(e))
            {
                map.put(e, map.get(e) + 1);
            }
        }
        int max = 0;
        int num = 0;
        for(int e : map.keySet())
        {
            if (max < map.get(e))
            {
                max = map.get(e);
                num = e;
            }
        }
        return num;
    }
    public void remove(HashMap<Integer, Integer> map)
    {
        ArrayList<Integer> list = new  ArrayList<>();
        for(int e : map.keySet())
        {
            if (map.get(e) == 1)
            {
                list.add(e);
            }
        }
        for (int e : list)
        {
            map.remove(e);
        }
    }

13 Minimum Window Substring

维护字典。个数，如有，计算个数，如等，左移，

    public String minWindow(String s, String t) {
        // write your code
        if (s == null || s.length() == 0)
        {
            return "";
        }
        //把t中的元素放入字典中
        HashMap<Character, Integer> hm = new HashMap<Character, Integer>();
        for (int i = 0; i < t.length(); i++)
        {
            char c = t.charAt(i);
            hm.put(c,hm.containsKey(c)? hm.get(c)+1:1);
        }
        int count = 0;
        int l = 0;
        int r = 0;
        int minL = s.length() + 1;
        int minStart = 0;
        for (r = 0; r < s.length(); r++)
        {
            if (hm.containsKey(s.charAt(r)))
            {
                hm.put(s.charAt(r), hm.get(s.charAt(r)) - 1);
                if (hm.get(s.charAt(r)) >= 0)
                {
                    count ++;
                }
                while (count == t.length())
                {
                    if (minL > r - l + 1)
                    {
                        minL = r - l + 1;
                        minStart = l;
                    }
                    if (hm.containsKey(s.charAt(l)))
                    {
                        hm.put(s.charAt(l), hm.get(s.charAt(l)) + 1);
                        if (hm.get(s.charAt(l)) > 0)
                        {
                            count --;
                        }
                    }
                    l++;
                }
            }
        }
        if (minL > s.length())
        {
            return "";
        }
        return s.substring(minStart, minStart + minL);
    }