Contianer
Stack
Last in first out
empty()
size()
top()
queue uses "front()".
push()
pop()
swap()
[Hard] No.42 Trapping Rain Water
Approach: Stack
Time Complexity: O(N), where N is the number of the list.
Space Complexity: O(N), where N is worst case of the size of stack.
Parentheses related question
Concept
Whenever you encounter an OPENING bracket (LEFT side) i.e. '(', '[', '{', executer PUSH.
Whenever you encounter an CLOSING bracket (RIGHT side) i.e. ')', ']', '}', executer POP.
[Easy] No.20 Valid Parentheses
Approach: Stack
Time Complexity: O(N), where N is the length of string.
Space Complexity: O(N), where N is the length of string.
Approach: Stack + map
Time Complexity: O(N^2), where N is the length of formula.
Space Complexity: O(N), where N is the length of formula.