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Implement the following operations of a stack using queues.
push
to back, peek/pop from front, size,
and is emptyoperations are valid.Update (2015-06-11):
The class name of the Java function had been updated to MyStack instead of Stack.
Credits:
Special thanks to @jianchao.li.fighter for adding this problem and all test cases.
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c++ code:
class Stack {
public:
// Push element x onto stack.
void push(int x) {
q1.push(x);
}
// Removes the element on top of the stack.
void pop() {
while(q1.size() > 1) {
int tmp = q1.front();
q1.pop();
q2.push(tmp);
}
q1.pop();
while(!q2.empty()) {
int tmp = q2.front();
q2.pop();
q1.push(tmp);
}
}
// Get the top element.
int top() {
while(q1.size() > 1) {
int tmp = q1.front();
q1.pop();
q2.push(tmp);
}
int ret = q1.front();
int t = q1.front();
q1.pop();
q2.push(t);
while(!q2.empty()) {
int tmp = q2.front();
q2.pop();
q1.push(tmp);
}
return ret;
}
// Return whether the stack is empty.
bool empty() {
return q1.empty() && q2.empty();
}
private:
queue<int> q1,q2;
};LeetCode:Implement Stack using Queues
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原文地址：http://blog.csdn.net/itismelzp/article/details/51331397
