代码随想录Day06 | Leetcode 242.有效的字母异位词 、Leetcode 349.两个数组的交集、Leetcode 202.快乐数、Leetcode1.两数之和

242.有效的字母异位词

class Solution {
    public boolean isAnagram(String s, String t) {
        if (s.length() != t.length()) {
            return false;
        }
        Map<String, Integer> hashMap = new HashMap<>();
        String[] s1 = s.split("");
        for (int i = 0; i < s1.length; i++) {
            hashMap.put(s1[i], hashMap.getOrDefault(s1[i], 0) + 1);
        }
        String[] t1 = t.split("");
        for (int i = 0; i < t1.length; i++) {
            if (!hashMap.containsKey(t1[i])) {
                return false;
            }
            hashMap.put(t1[i], hashMap.get(t1[i]) - 1);

        }
        Iterator iterator = hashMap.keySet().iterator();
        while (iterator.hasNext()) {
            Object key = iterator.next();
            if (hashMap.get((String) key) != 0) {
                return false;
            }
        }

        return true;
    }
}

349.两个数组的交集

class Solution {
    public int[] intersection(int[] nums1, int[] nums2) {
        Set<Integer> hashSet = new HashSet<>();
        for (int i = 0; i < nums1.length; i++) {
            hashSet.add(nums1[i]);
        }
        Set<Integer> set = new HashSet<>();
        for (int i = 0; i < nums2.length; i++) {
            if (hashSet.contains(nums2[i])) {
                set.add(nums2[i]);
            }
        }
        //Set[] 转int[]
        int[] res = set.stream().mapToInt(Integer::intValue).toArray();
        return res;
    }
}

202.快乐数

class Solution {
    public boolean isHappy(int n) {
        int temp = n;
        Set<Integer> hashSet = new HashSet<>();
        while (true) {
            int sum = sumEvery(temp);
            temp = sum;
            if (sum == 1) {
                break;
            }
            System.out.println("sum = " + sum);
            if (hashSet.contains(sum)) {
                return false;
            }
            hashSet.add(sum);
        }

        return true;
    }

    public int sumEvery(int n) {
        int sum = 0;
        do {
            int p = n % 10;
            sum += p * p;
            n /= 10;
        } while (n > 0);
        return sum;
    }
}

1.两数之和

class Solution {
    public int[] twoSum(int[] nums, int target) {
        Map<Integer, Integer> hashMap = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            hashMap.put(target - nums[i], i);
        }
        int[] res = new int[2];
        for (int i = 0; i < nums.length; i++) {

            //同时要判断是否是同一个下标hashMap.get(nums[i]) != i
            if (hashMap.containsKey(nums[i]) && hashMap.get(nums[i]) != i) {
                res[0] = i;
                res[1] = hashMap.get(nums[i]);
                break;
            }
        }

        return res;
    }
}