LeetCode-Easy刷题(33) Min Stack

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.

创建一个栈对象,实现相应的方法.

public class MinStack {    private int top = 0;    private int[] stack;    private int[] minStack;    private int minTop=-1;    /** initialize your data structure here. */    public MinStack() {        stack = new int[8];        minStack = new int[8];    }    public void push(int x) {        stack[top] = x;        if(minTop <0 ||minStack[minTop] >=x){            minTop++;            minStack[minTop] = x;        }        if(minTop>=minStack.length-1){            int[] newStack = new int[top*2];            for (int i = 0; i < minStack.length; i++) {                newStack[i] = minStack[i];            }            minStack = newStack;        }        top++;        if(top >=stack.length){            int[] newStack = new int[top*2];            for (int i = 0; i < stack.length; i++) {                newStack[i] = stack[i];            }            stack = newStack;        }    }    public void pop() {        int remove = stack[top-1];        stack[top-1]=0;        top--;        if(remove ==minStack[minTop]){            minStack[minTop] = 0;            minTop--;        }    }    public int top() {        return stack[top-1];    }    public int getMin() {        return minStack[minTop];    }}