Programming

Maintain two stacks in parallel: one for values and one tracking the current minimum at each level. This makes `getMin` O(1) instead of scanning the full stack, and avoids rebuilding the array on every `pop`.

Push opening brackets onto a stack; for each closing bracket, check if it matches the top. If the stack is empty at the end, the string is valid. O(n) time versus the string-slicing approach, which rebuilds the string on every matched pair.

Use a stack to simulate the game: push scores for numbers, `D`, and `+`, pop for `C`. After processing all operations, sum the remaining stack. Straightforward O(n) simulation with no tricky edge cases.

Pre-allocate an array of double length, then fill both halves in a single pass — writing each element at index `i` and `i + n`. Runs in O(n) time with a clean, spread-free approach.

Traverse the array right to left, tracking the running maximum. Each element gets replaced with the current max before updating it. This avoids the inner loop, reducing time complexity from O(n²) to O(n) with O(1) space.