题解 | 最大体重的牛

1. 一个辅助栈，记录每次压栈时最大值。

import java.util.*;

public class Solution {
    static class MaxCowStack {
        Deque<Integer> stack;
        Deque<Integer> maxStack;

        public MaxCowStack() {
            stack = new ArrayDeque<>();
            maxStack = new ArrayDeque<>();
        }

        public void push(int id, int weight) {
            stack.addLast(weight);
            if (!maxStack.isEmpty() && maxStack.getLast() > weight) {
                maxStack.addLast(maxStack.getLast());
            } else {
                maxStack.addLast(weight);
            }
        }
        
        public void pop() {
            stack.removeLast();
            maxStack.removeLast();
        }

        public int top() {
            return stack.getLast();
        }

        public int getMax() {
            return maxStack.getLast();
        }
    }
    public int[] max_weight_cow (String[] op, int[][] vals) {
        int[] ans = new int[op.length];
        MaxCowStack stack = null;
        for (int i = 0; i < op.length; i++) {
            String s = op[i];
            switch (s) {
                case "MaxCowStack":
                    stack = new MaxCowStack();
                    ans[i] = -1;
                    break;
                case "push":
                    stack.push(vals[i][0], vals[i][1]); 
                    ans[i] = -1;
                    break;
                case "pop":
                    stack.pop();
                    ans[i] = -1;
                    break;
                case "top":
                    ans[i] = stack.top();
                    break;
                case "getMax":
                    ans[i] = stack.getMax();
                    break;
            }
        }
        return ans;
    }
}