leetcode- 232. Implement Queue using Stacks
使用栈实现队列:
将栈中的元素取出再存入一次就是队列:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 | class MyQueue { public : /** Initialize your data structure here. */ MyQueue() { } /** Push element x to the back of queue. */ void push( int x) { s.push(x); } /** Removes the element from in front of queue and returns that element. */ int pop() { stack< int > s1; while (!s.empty()) { int t=s.top(); s.pop(); s1.push(t); } int t=s1.top(); s1.pop(); while (!s1.empty()) { int t=s1.top(); s.push(t); s1.pop(); } return t; } /** Get the front element. */ int peek() { stack< int > s_tem=s; while (s_tem.size()>1) { s_tem.pop(); } return s_tem.top(); } /** Returns whether the queue is empty. */ bool empty() { return s.empty(); } private : stack< int > s; }; /** * Your MyQueue object will be instantiated and called as such: * MyQueue obj = new MyQueue(); * obj.push(x); * int param_2 = obj.pop(); * int param_3 = obj.peek(); * bool param_4 = obj.empty(); */ |
更简单一点实现,pop和top的实现互相借助时:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 | class MyQueue { public : stack< int > S1, S2; /** Initialize your data structure here. */ MyQueue() { } /** Push element x to the back of queue. */ void push( int x) { S1.push(x); } /** Removes the element from in front of queue and returns that element. */ int pop() { int v = -1; if (!S2.empty()) { v = S2.top(); S2.pop();} else { while (!S1.empty()) { S2.push(S1.top()); S1.pop(); } v = S2.top(); S2.pop(); } return v; } /** Get the front element. */ int peek() { if (!S2.empty()) return S2.top(); else { while (!S1.empty()) { S2.push(S1.top()); S1.pop(); } return S2.top(); } } /** Returns whether the queue is empty. */ bool empty() { return (S1.empty()) && (S2.empty()); } }; /** * Your MyQueue object will be instantiated and called as such: * MyQueue obj = new MyQueue(); * obj.push(x); * int param_2 = obj.pop(); * int param_3 = obj.peek(); * bool param_4 = obj.empty(); */ |
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