Basic Two-Pointer Questions

void reverseString(vector<char>& s) {
    int l = 0, r = s.size() - 1;
    while (l < r) swap(s[l++], s[r--]);
}

def reverse_string(s):
    l, r = 0, len(s) - 1
    while l < r:
        s[l], s[r] = s[r], s[l]
        l += 1; r -= 1

public void reverseString(char[] s) {
    int l = 0, r = s.length - 1;
    while (l < r) {
        char tmp = s[l]; s[l] = s[r]; s[r] = tmp;
        l++; r--;
    }
}

bool isPalindrome(string s) {
    int l = 0, r = s.size() - 1;
    while (l < r) {
        while (l < r && !isalnum(s[l])) l++;
        while (l < r && !isalnum(s[r])) r--;
        if (tolower(s[l]) != tolower(s[r])) return false;
        l++; r--;
    }
    return true;
}

def is_palindrome(s):
    l, r = 0, len(s) - 1
    while l < r:
        while l < r and not s[l].isalnum(): l += 1
        while l < r and not s[r].isalnum(): r -= 1
        if s[l].lower() != s[r].lower(): return False
        l += 1; r -= 1
    return True

public boolean isPalindrome(String s) {
    int l = 0, r = s.length() - 1;
    while (l < r) {
        while (l < r && !Character.isLetterOrDigit(s.charAt(l))) l++;
        while (l < r && !Character.isLetterOrDigit(s.charAt(r))) r--;
        if (Character.toLowerCase(s.charAt(l)) != Character.toLowerCase(s.charAt(r))) return false;
        l++; r--;
    }
    return true;
}

def two_sum(numbers, t):
    l, r = 0, len(numbers) - 1
    while l < r:
        s = numbers[l] + numbers[r]
        if s == t: return [l + 1, r + 1]
        if s < t:  l += 1
        else:      r -= 1

void moveZeroes(vector<int>& nums) {
    int write = 0;
    for (int read = 0; read < (int)nums.size(); read++) {
        if (nums[read] != 0) nums[write++] = nums[read];
    }
    while (write < (int)nums.size()) nums[write++] = 0;
}

def move_zeroes(nums):
    write = 0
    for read in range(len(nums)):
        if nums[read] != 0:
            nums[write] = nums[read]; write += 1
    for i in range(write, len(nums)):
        nums[i] = 0

public void moveZeroes(int[] nums) {
    int write = 0;
    for (int read = 0; read < nums.length; read++) {
        if (nums[read] != 0) nums[write++] = nums[read];
    }
    while (write < nums.length) nums[write++] = 0;
}

def middle_node(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
    return slow

bool hasCycle(ListNode* head) {
    ListNode *slow = head, *fast = head;
    while (fast && fast->next) {
        slow = slow->next;
        fast = fast->next->next;
        if (slow == fast) return true;
    }
    return false;
}

def has_cycle(head):
    slow = fast = head
    while fast and fast.next:
        slow = slow.next
        fast = fast.next.next
        if slow == fast: return True
    return False

public boolean hasCycle(ListNode head) {
    ListNode slow = head, fast = head;
    while (fast != null && fast.next != null) {
        slow = slow.next;
        fast = fast.next.next;
        if (slow == fast) return true;
    }
    return false;
}