用兩個棧實現一個隊列。隊列的聲明如下,請實現它的兩個函數 appendTail 和 deleteHead ,分別完成在隊列尾部插入整數和在隊列頭部刪除整數的功能。(若隊列中沒有元素,deleteHead 操作返回 -1 )
示例 1:
輸入:
["CQueue","appendTail","deleteHead","deleteHead"]
[[],[3],[],[]]
輸出:[null,null,3,-1]
示例 2:
輸入:
["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
[[],[],[5],[2],[],[]]
輸出:[null,-1,null,null,5,2]
提示:
1 <= values <= 10000
最多會對 appendTail、deleteHead 進行 10000 次調用
來源:力扣(LeetCode)
鏈接:https://leetcode-cn.com/problems/yong-liang-ge-zhan-shi-xian-dui-lie-lcof
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public class CQueue {
Stack<Integer> stack1;
Stack<Integer> stack2;
public CQueue() {
stack1 = new Stack<>();
stack2 = new Stack<>();
}
public void appendTail(int value) {
stack1.add(value);
}
public int deleteHead() {
if (stack2.isEmpty()) {
if (stack1.isEmpty())
return -1;
while (!stack1.isEmpty()) {
stack2.add(stack1.pop());
}
return stack2.pop();
} else {
return stack2.pop();
}
}
}
//換用LinkedList類,速度得到提升
class CQueue {
LinkedList<Integer> stack1;
LinkedList<Integer> stack2;
public CQueue() {
stack1 = new LinkedList<>();
stack2 = new LinkedList<>();
}
public void appendTail(int value) {
stack1.add(value);
}
public int deleteHead() {
if (stack2.isEmpty()) {
if (stack1.isEmpty())
return -1;
while (!stack1.isEmpty()) {
stack2.add(stack1.pop());
}
return stack2.pop();
} else {
return stack2.pop();
}
}
}