[LeetCode] 155. Min Stack

轉自LeetCode

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

Example:

MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin();   --> Returns -3.
minStack.pop();
minStack.top();      --> Returns 0.
minStack.getMin();   --> Returns -2.

<Solution>

這題要用兩個 stack 來實做

一個就是正常的 stack，一個是存放該階段最小值的 stack

分開來處理就可以了

code 如下

	class MinStack {
	public:
	/** initialize your data structure here. */
	MinStack() {
	}
	void push(int x) {
	if(minStk.empty() || (x <= minStk.top())) {
	minStk.push(x);
	}
	normalStk.push(x);
	}
	void pop() {
	if(normalStk.top() == minStk.top()) {
	minStk.pop();
	}
	normalStk.pop();
	}
	int top() {
	return normalStk.top();
	}
	int getMin() {
	return minStk.top();
	}
	private:
	stack<int> normalStk, minStk;
	};

view raw minStack.cpp hosted with ❤ by GitHub