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Copy pathimplement-stack-using-queues.cpp
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72 lines (64 loc) · 1.67 KB
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class MyStack {
queue<int> q1, q2;
public:
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
if(!q1.empty()) q1.push(x);
else if(!q2.empty()) q2.push(x);
else
q1.push(x);
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
if(q1.empty()){
while(!q2.empty()){
int front = q2.front();
q2.pop();
if(q2.empty()) return front;
q1.push(front);
}
}
else{
while(!q1.empty()){
int front = q1.front();
q1.pop();
if(q1.empty()) return front;
q2.push(front);
}
}
}
/** Get the top element. */
int top() {
if(q1.empty()){
while(!q2.empty()){
int front = q2.front();
q1.push(front);
q2.pop();
if(q2.empty()) return front;
}
}
else{
while(!q1.empty()){
int front = q1.front();
q2.push(front);
q1.pop();
if(q1.empty()) return front;
}
}
}
/** Returns whether the stack is empty. */
bool empty() {
return q1.empty() && q2.empty();
}
};
/**
* 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();
* bool param_4 = obj.empty();
*/