Here's a test case generator for the given problem statement "A: Information Search":

```python
import random

def tcgen():
    # Generate lengths of the posting lists n and m
    n = random.randint(1, 2 * 10**5)
    m = random.randint(1, 2 * 10**5)
    
    # Generate posting lists a and b
    a = sorted(random.sample(range(1, 10**9 + 1), n))
    b = sorted(random.sample(range(1, 10**9 + 1), m))
    
    return n, m, a, b

# Example usage
if __name__ == "__main__":
    n, m, a, b = tcgen()
    print(n, m)
    print(" ".join(map(str, a)))
    print(" ".join(map(str, b)))
```

### Explanation:
1. **Lengths of Posting Lists (`n` and `m`)**:
   - Randomly generate `n` and `m` within the given constraints (1 ≤ `n`, `m` ≤ 2 × 10^5).

2. **Posting Lists (`a` and `b`)**:
   - Use `random.sample` to generate unique values within the range [1, 10^9] for both lists `a` and `b`.
   - Ensure the lists are sorted, as per the problem constraints.

3. **Return Values**:
   - The function returns the lengths of the lists (`n`, `m`) and the actual lists (`a`, `b`).

4. **Example Usage**:
   - The provided example usage demonstrates how to call the `tcgen` function and print the generated test case.

By running this script, you can generate random test cases that follow the given problem constraints.