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剑指 Offer 09. 用两个栈实现队列
2022-07-05 08:16:00 【程序员·小李】
用两个栈实现一个队列。队列的声明如下,请实现它的两个函数 appendTail 和 deleteHead ,分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素,deleteHead 操作返回 -1 )
示例 1:
输入:
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
输出:[null,null,3,-1]
示例 2:
输入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
输出:[null,-1,null,null,5,2]
提示:
1 <= values <= 10000
最多会对 appendTail、deleteHead 进行 10000 次调用
思路:
1. 一个插入栈,一个输出栈。插入数据时,往插入栈中写。
2. 输出数据时,优先从输出栈弹出,如果输出栈中不存在,则依次从输入栈中压入。
class CQueue {
Stack<Integer> pushStack = new Stack<Integer>();
Stack<Integer> popStack = new Stack<Integer>();
public CQueue() {
}
public void appendTail(int value) {
pushStack.push(value);
}
public int deleteHead() {
if (popStack.empty()){
while (!pushStack.empty()){
popStack.push(pushStack.pop());
}
}
if (popStack.empty()){
return -1;
}
return popStack.pop();
}
}
/**
* Your CQueue object will be instantiated and called as such:
* CQueue obj = new CQueue();
* obj.appendTail(value);
* int param_2 = obj.deleteHead();
*/
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