public static int[] intersection(int[] nums1, int[] nums2) {
    Set<Integer> set1 = new HashSet<>();
    Set<Integer> set2 = new HashSet<>();
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    for (int i : nums1) {
        set1.add(i);
    }
    for (int i : nums2) {
        if (set1.contains(i)) {
            set2.add(i);
        }
    }
    int[] ints = set2.stream().mapToInt(s -> s).toArray();
    return ints;
}
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public static int[] intersect(int[] nums1, int[] nums2) {
    Arrays.sort(nums1);
    Arrays.sort(nums2);
    int i = 0,j = 0, z = 0;
    int x = nums1.length < nums2.length ? nums1.length: nums2.length;
    int[] result = new int[x];
    while(j < nums2.length && i < nums1.length){
        if (nums1[i] == nums2[j]){
            result[z] = nums1[i];
            i++;
            j++;
            z++;
        } else if (nums1[i] < nums2[j]) {
            i++;
        }else{
            j++;
        }
    }
    int[] ints = Arrays.copyOf(result, z);
    return ints;
}
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public static boolean isHappy(int n) {
    Set<Integer> set = new HashSet<>();
    while(n != 1 && !set.contains(n)){
        set.add(n);
        n = test(n);
    }
    return n == 1;
}
private static Integer test(int n){
    int result = 0;
    while(n > 0){
        int temp = n % 10;
        result += temp * temp;
        n = n / 10;
    }
    return result;
}
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public static  int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums.length; i++) {
        int temp = target - nums[i];
        if (map.containsKey(temp)) {
            return new int[]{i, map.get(temp)};
        }else{
            map.put(nums[i], i);
        }
    }
    return null;
}
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public static int fourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
    Map<Integer, Integer> map = new HashMap<>();
    int num = 0;
    for (int i = 0; i < nums1.length; i++) {
        for (int j = 0; j < nums2.length; j++) {
            num = nums1[i] + nums2[j];
            int count = map.getOrDefault(num, 0) + 1;
            map.put(num, count);
        }
    }
    int result = 0;
    for (int i = 0; i < nums3.length; i++) {
        for (int j = 0; j < nums4.length; j++) {
            num = 0 - (nums3[i] + nums4[j]);
            int count = map.getOrDefault(num, 0);
            result += count;
        }
    }
    return result;
}
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public static List<List<Integer>> threeSum(int[] nums) {
    List<List<Integer>> result = new ArrayList<>();
    Arrays.sort(nums);
    for (int i = 0; i < nums.length; i++) {
        if (nums[i] > 0) {
            return result;
        }
        if (i > 0 && nums[i] == nums[i - 1]){
            continue;
        }
        int left = i + 1;
        int right = nums.length - 1;
        while (left < right){
            int sum = nums[i] + nums[left] + nums[right];
            if (sum < 0){
                left++;
            }else if (sum > 0){
                right--;
            }else{
                result.add(Arrays.asList(nums[i], nums[left], nums[right]));
                while(right > left && nums[right] == nums[right - 1]) right--;
                while(right > left && nums[left] == nums[left + 1]) left++;
                right--;
                left++;
            }
        }
    }
    return result;
}
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public static List<List<Integer>> fourSum(int[] nums, int target) {
    List<List<Integer>> list = new ArrayList<>();
    Arrays.sort(nums);
    for (int i = 0; i < nums.length; i++) {
        if (nums[i] > target && (nums[i] > 0 || target > 0)){
            return list;
        }
        if (i > 0 && nums[i] == nums[i - 1]){
            continue;
        }
        for (int j = nums.length - 1; j > i; j--) {
            if (j < nums.length - 1 && nums[j] == nums[j + 1]){
                continue;
            }
            int left = i + 1;
            int right = j - 1;
            while (left < right){
                long num = (long) nums[i] + nums[left] + nums[right] + nums[j];
                if (num < target){
                    left++;
                }else if (num > target){
                    right--;
                }else{
                    list.add(Arrays.asList(nums[i],nums[left],nums[right],nums[j]));
                    while(left < right && nums[right] == nums[right - 1]) right--;
                    while(left < right && nums[left] == nums[left + 1]) left++;
                    left++;
                    right--;
                }
            }
        }
    }
    return list;
}
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public static void reverseString(char[] s) {
    for (int i = 0; i < s.length / 2; i++) {
        char temp = s[i];
        s[i] = s[s.length - 1 - i];
        s[s.length - 1 - i] = temp;
    }
}
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public static String reverseStr(String s, int k) {
    char[] chars = s.toCharArray();
    int left = 0;
    int right = left + 2 * k;
    while (right < s.length()){
        int stop = left + k - 1;
        while(left < stop){
            char temp = chars[left];
            chars[left] = chars[stop];
            chars[stop] = temp;
            left++;
            stop--;
        }
        left = right;
        right += 2 * k;
    }
    right = s.length() - left < k ? s.length() - 1 : left + k -1 ;
    while (left < right){
        char temp = chars[left];
        chars[left] = chars[right];
        chars[right] = temp;
        left++;
        right--;
    }
    return String.valueOf(chars);
}
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public static String replaceSpace(String s) {
    char[] chars = s.toCharArray();
    int length = s.length();
    for (int i = 0; i < chars.length; i++) {
        if (chars[i] == ' '){
            length += 2;
        }
    }
    char[] ints = new char[length];
    for (int i = chars.length - 1; i >= 0; i--) {
        if (i == length){
            return String.valueOf(ints);
        }
        if (chars[i] == ' '){
            ints[--length] = '0';
            ints[--length] = '2';
            ints[--length] = '%';
        }else{
            ints[--length] = chars[i];
        }
        System.out.println(Arrays.toString(ints));
    }
    return String.valueOf(ints);
}
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public static String reverseWords(String s) {
    List<String> list = new ArrayList<>();
    char[] chars = s.toCharArray();
    for (int i = 0; i < chars.length; i++) {
        StringBuilder str = new StringBuilder();
        while(i < chars.length && chars[i] != ' '){
            str.append(chars[i]);
            i++;
        }
        if (str != null){
            list.add(str.toString());
        }
    }
    StringBuilder str = new StringBuilder();
    for (int i = list.size() - 1; i >= 0; i--) {
        str.append(list.get(i));
        str.append(" ");
    }
    str.deleteCharAt(str.length() - 1);
    return str.toString();
}
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