代码随想录算法训练营Day9

232.用栈实现队列

Collection——List——Vector类——Stack类

class MyQueue {Stack<Integer> stackIn;Stack<Integer> stackOut;public MyQueue() {stackIn=new Stack();stackOut=new Stack();} public void push(int x) {stackIn.push(x);}public int pop() {notempty();return stackOut.pop();}public int peek() {notempty();return stackOut.peek();}public boolean empty() {if(stackIn.isEmpty()&&stackOut.isEmpty())return true;elsereturn false;}public void notempty(){if(!stackOut.isEmpty())return;while(!stackIn.isEmpty()){stackOut.push(stackIn.pop());}}
}/*** Your MyQueue object will be instantiated and called as such:* MyQueue obj = new MyQueue();* obj.push(x);* int param_2 = obj.pop();* int param_3 = obj.peek();* boolean param_4 = obj.empty();*/

225. 用队列实现栈

Collection——Queue——LinkedList类

class MyStack {Queue<Integer> myStack;public MyStack() {myStack=new LinkedList();}public void push(int x) {myStack.offer(x);int size=myStack.size();for(int i=0;i<size-1;i++){myStack.offer(myStack.poll());}}  public int pop() {return myStack.poll();} public int top() {return myStack.peek();}public boolean empty() {return myStack.isEmpty();}
}
/*** Your MyStack object will be instantiated and called as such:* MyStack obj = new MyStack();* obj.push(x);* int param_2 = obj.pop();* int param_3 = obj.top();* boolean param_4 = obj.empty();*/

20. 有效的括号

Collection——Deque——LinkedList类

class Solution {public boolean isValid(String s) {Deque<Character> mystack=new LinkedList();char a;char[] ch=s.toCharArray();for(int i=0;i<ch.length;i++){a=ch[i];if(a=='('){mystack.push(')');}else if(a=='{'){mystack.push('}');}else if(a=='['){mystack.push(']');}else if(mystack.isEmpty()||mystack.peek()!=a){return false;}else{mystack.pop();  }}return mystack.isEmpty();}
}

1047. 删除字符串中的所有相邻重复项

StringBuilder(StringBuffer)

class Solution {public String removeDuplicates(String s) {StringBuffer sb=new StringBuffer();int index=-1;for(int i=0;i<s.length();i++){         char ch=s.charAt(i);if(sb.length()==0||sb.charAt(index)!=ch){index++;sb.append(ch);}else{sb.deleteCharAt(index);index--;}}return sb.toString();}
}