特殊数据结构之使用Java实现单调栈示例

    import java.util.ArrayList;  
    import java.util.Stack;  
    public class MonotonicStack {  
        private Stack<Integer> stack;  
        private Stack<Integer> maxStack;  
        public MonotonicStack() {  
            stack = new Stack<>();  
            maxStack = new Stack<>();  
        }  
        public void push(int val) {  
            if (val >= stack.peek()) {  
                stack.push(val);  
            } else {  
                while (!maxStack.isEmpty() && val > maxStack.peek()) {  
                    maxStack.pop();  
                }  
                stack.push(val);  
                maxStack.push(val);  
            }  
        }  
        public int pop() {  
            if (!stack.isEmpty()) {  
                return stack.pop();  
            } else {  
                return -1;  
            }  
        }  
        public int top() {  
            if (!stack.isEmpty()) {  
                return stack.peek();  
            } else {  
                return -1;  
            }  
        }  
        public boolean isEmpty() {  
            return stack.isEmpty();  
        }  
    }