LeetCode155.最小栈

设计一个支持 push，pop，top 操作，并能在常数时间内检索到最小元素的栈。

push(x) -- 将元素 x 推入栈中。
pop() -- 删除栈顶的元素。
top() -- 获取栈顶元素。
getMin() -- 检索栈中的最小元素。

示例:

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

class MinStack {

    private Stack<Integer> stack;
    private Stack<Integer> stackMin;
    /** initialize your data structure here. */
    public MinStack() {
        this.stack = new Stack<Integer>();
        this.stackMin = new Stack<Integer>();
    }
    
    public void push(int x) {
        stack.push(x);
        if (!stackMin.isEmpty()) {
            int min = stackMin.peek();
            if (x<=min) {
                stackMin.push(x);
            }
        } else {
            this.stackMin.push(x);
        }
    }
    
    public void pop() {
        int value = this.stack.pop();
        if (!this.stackMin.isEmpty()) {
            if (value == stackMin.peek()) {
                stackMin.pop();
            }
        }
    }
    
    public int top() {
        int value = this.stack.peek();
        return value;
    }
    
    public int getMin() {
        return this.stackMin.peek();
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */

LeetCode155.最小栈

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