數據結構之棧應用，和網易大佬的技術面談

 int num2=0;
for(String str:tokens){
if(str.equals("+")){
num1=stack.pop();
num2=stack.pop();
stack.push(num1+num2);
}else if(str.equals("-")){
num1=stack.pop();
num2=stack.pop();
stack.push(num2-num1);
}else if(str.equals("*")){
num1=stack.pop();
num2=stack.pop();
stack.push(num1*num2);
}else if(str.equals("/")){
num1=stack.pop();
num2=stack.pop();
stack.push(num2/num1);
}else{
stack.push(Integer.parseInt(str));
}
}
return stack.pop();
}

### [](
)1.3用棧實現隊列
[leetcode 232 題](
)
用棧模擬出隊列的push(),pop(),peek(),empty() 方法


1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.

public Stack<Integer> stack1;
public Stack<Integer> stack2;
/** Initialize your data structure here. */
public MyQueue() {
stack1 =new Stack<>();
stack2 =new Stack<>();
}
/** Push element x to the back of queue. */
public void push(int x) {
stack1.push(x);
}
/** Removes the element from in front of queue and returns that element. */
public int pop() {
if(stack2.empty()){
while(!stack1.empty()){
stack2.push(stack1.pop());
}
}
return stack2.pop();
}
/** Get the front element. */
public int peek() {
if(stack2.empty()){
while(!stack1.empty()){
stack2.push(stack1.pop());
}
}
return stack2.peek();
}
/** Returns whether the queue is empty. */
public boolean empty() {
return stack1.empty()&&stack2.empty();
}

### [](
)1.4最小棧
[leetcode 155題](
)


1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.

//定義雙棧來實現最小棧
public Deque<Integer> stack1;
public Deque<Integer> minStack;
/** initialize your data structure here. */
public MinStack() {
stack1=new LinkedList<Integer>();
minStack=new LinkedList<Integer>();
minStack.push(Integer.MAX_VALUE);
}
public void push(int val) {
stack1.push(val);
minStack.push(Math.min(val,minStack.peek()));
}
public void pop() {
stack1.pop();