232 用栈实现队列
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class MyQueue { public: stack<int> stIn; stack<int> stOut; MyQueue() { } void push(int x) { stIn.push(x); } int pop() { if(stOut.empty()){ while(!stIn.empty()){ stOut.push(stIn.top()); stIn.pop(); } } int result = stOut.top(); stOut.pop(); return result; } int peek() { if(stOut.empty()){ while(!stIn.empty()){ stOut.push(stIn.top()); stIn.pop(); } } int result = stOut.top(); return result; } bool empty() { if(stIn.empty() && stOut.empty()){ return true; }else{ return false; } } }; /** * 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(); */
225 用队列实现栈
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class MyStack { public: queue<int> q; MyStack() { } void push(int x) { q.push(x); } int pop() { for(int i = 1;i < q.size();i++){ q.push(q.front()); q.pop(); } int result = q.front(); q.pop(); return result; } int top() { int result = q.back(); return result; } bool empty() { if(q.empty()){ return true; }else{ return false; } } }; /** * 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(); */
20 有效括号
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class Solution { public: stack<char> stack; bool isValid(string s) { for(int i = 0; i < s.size();i++){ if(s[i] == '(' || s[i] == '[' || s[i] == '{'){ stack.push(s[i]); } if(s[i] == ')'){ if(!stack.empty() && stack.top() == '('){ stack.pop(); }else{ return false; } } if(s[i] == ']'){ if(!stack.empty() && stack.top() == '['){ stack.pop(); }else{ return false; } } if(s[i] == '}'){ if(!stack.empty() && stack.top() == '{'){ stack.pop(); }else{ return false; } } } if(stack.empty()){ return true; }else{ return false; } } };
class Solution { public: bool isValid(string s) { if (s.size() % 2 != 0) return false; // 如果s的⻓度为奇数，⼀定不符合要求 stack<char> st; for (int i = 0; i < s.size(); i++) { if (s[i] == '(') st.push(')'); else if (s[i] == '{') st.push('}'); else if (s[i] == '[') st.push(']'); else if (st.empty() || st.top() != s[i]) return false; else st.pop(); // st.top() 与 s[i]相等，栈弹出元素 } return st.empty(); } };
1047 删除字符串中的所有相邻重复项
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class Solution { public: stack<char> q; string removeDuplicates(string s) { for(int i = 0;i < s.size();i++){ if(!q.empty()){ if(s[i] == q.top()){ q.pop(); }else{ q.push(s[i]); } }else{ q.push(s[i]); } } string result; result.resize(q.size()); for(int i = q.size() - 1;i >= 0;i--){ result[i] = q.top(); q.pop(); } return result; } };
