题目
定义栈的数据结构,请在该类型中实现一个能够得到栈的最小元素的 min 函数在该栈中,调用 min、push 及 pop 的时间复杂度都是 O(1)。
示例:
MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.min(); --> 返回 -3. minStack.pop(); minStack.top(); --> 返回 0. minStack.min(); --> 返回 -2.
提示:
各函数的调用总次数不超过 20000 次
解题思路
class MinStack { var stackList:[Int] = [] var minRecordList:[Int] = [] /** initialize your data structure here. */ init() { } func push(_ x: Int) { stackList.append(x) if minRecordList.isEmpty { minRecordList.append(x) return } // 通过栈方式登记最少值 if x < minRecordList.last! { minRecordList.append(x) } else { minRecordList.append(minRecordList.last!) } } func pop() { stackList.popLast() minRecordList.popLast() } func top() -> Int { return stackList.last! } func min() -> Int { return minRecordList.last! } } /** * Your MinStack object will be instantiated and called as such: * let obj = MinStack() * obj.push(x) * obj.pop() * let ret_3: Int = obj.top() * let ret_4: Int = obj.min() */ let obj = MinStack() obj.push(5) obj.push(4) obj.pop() let ret_3: Int = obj.top() obj.push(3) let ret_4: Int = obj.min()