代码随想录算法训练营第五天| LeetCode242.有效的字母异位词、349. 两个数组的交集、202. 快乐数、1. 两数之和

 public boolean anagram(String s, String t) {
        int[] dic = new int[26];
        if (s.length() != t.length()) {
            return false;
        }
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            dic[c - 'a']++;
            char c1 = t.charAt(i);
            dic[c1 - 'a']--;
        }
        for (int i = 0; i < 26; i++) {
            if (dic[i] != 0) {
                return false;
            }
        }
        return true;
  }

    public int[] intersection(int[] nums1, int[] nums2) {
        byte[] dic1 = new byte[1100];
        byte[] dic2 = new byte[1100];
        for (int i : nums1) {
            dic1[i] = 1;
        }
        for (int i : nums2) {
            dic2[i] = 1;
        }
        List<Integer> list = new ArrayList<>();
        for (int i = 0; i <= 1000; i++) {
            if (dic1[i] == 1 && dic2[i] == 1) {
                list.add(i);
            }
        }
        return list.stream().mapToInt(Integer::intValue).toArray();
    }

    public int[] intersection(int[] nums1, int[] nums2) {
        byte[] dic1 = new byte[1100];
        Set<Integer> set = new HashSet<>();
        for (int i : nums1) {
            dic1[i] = 1;
        }
        for (int i : nums2) {
            if (dic1[i] == 1) {
                set.add(i);
            }
        }
        return set.stream().mapToInt(Integer::intValue).toArray();
    }

    public int[] intersection2(int[] nums1, int[] nums2) {
        Set<Integer> set = new HashSet<>();
        for (int i : nums1) {
            set.add(i);
        }
        Set<Integer> res = new HashSet<>();
        for (int i : nums2) {
            if (set.contains(i)) {
                res.add(i);
            }
        }
        return res.stream().mapToInt(x -> x).toArray();
    }

public boolean isHappy(int n) {
        int sum = getSum(n);
        while (true) {
            if (sum == 1) {
                return true;
            } else {
                sum = getSum(sum);
            }
        }
    }

    private int getSum(int n) {
        int sum = 0;
        while (n != 0) {
            sum += (n % 10) * (n % 10);
            n = n / 10;
        }
        return sum;
    }

public boolean isHappy(int n) {
        //只要记录下sum，如果重复出现了，说明肯定会进入死循环
        Set<Integer> set = new HashSet<>();
        int sum = getSum(n);
        while (sum != 1) {
            if (set.contains(sum)) {
                return false;//set包含这个值就直接返回
            } else {
                set.add(sum);//set不包含这个sum值就加入进来
            }
            sum = getSum(sum);
        }
        return true;
    }

    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> map = new HashMap<>();
        int[] res = new int[2];
        for (int i = 0; i < nums.length; i++) {
            if (!map.containsKey(target - nums[i])) {
                map.put(nums[i], i);
            } else {
                res[0] = map.get(target - nums[i]);//取出余数的下标
                res[1] = i;//当前数的下标
            }
        }
        return res;
    }