155. Min Stack
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
- push(x) -- Push element x onto stack.
- pop() -- Removes the element on top of the stack.
- top() -- Get the top element.
- getMin() -- Retrieve the minimum element in the stack.
Example:
MinStack minStack = new MinStack(); minStack.push(-2); minStack.push(0); minStack.push(-3); minStack.getMin(); --> Returns -3. minStack.pop(); minStack.top(); --> Returns 0. minStack.getMin(); --> Returns -2.
设计一个栈，有一个取最小元素的操作
C++（29ms）： 用两个栈
1 class MinStack { 2 private: 3 stack<int> s1 ; 4 stack<int> s2 ; 5 public: 6 void push(int x) { 7 s1.push(x) ; 8 if (s2.empty() || x <= getMin()) 9 s2.push(x) ; 10 } 11 12 void pop() { 13 if (s1.top() == getMin()) 14 s2.pop() ; 15 s1.pop() ; 16 } 17 18 int top() { 19 return s1.top() ; 20 } 21 22 int getMin() { 23 return s2.top() ; 24 } 25 }; 26 27 /** 28 * Your MinStack object will be instantiated and called as such: 29 * MinStack obj = new MinStack(); 30 * obj.push(x); 31 * obj.pop(); 32 * int param_3 = obj.top(); 33 * int param_4 = obj.getMin(); 34 */
C++(29ms): 一个栈 注意用long
1 class MinStack { 2 private: 3 stack<long> s ; 4 5 long Min ; 6 public: 7 void push(int x) { 8 if (s.empty()){ 9 s.push(0) ; 10 Min = x ; 11 }else{ 12 s.push(x-Min) ; 13 if (x < Min) 14 Min = x ; 15 } 16 } 17 18 void pop() { 19 if (s.empty()) 20 return ; 21 long top = s.top() ; 22 if (top < 0) 23 Min -= top ; 24 s.pop() ; 25 } 26 27 int top() { 28 long top = s.top() ; 29 if (top > 0){ 30 return (int)top+Min ; 31 }else{ 32 return (int)Min ; 33 } 34 } 35 36 int getMin() { 37 return (int)Min ; 38 } 39 }; 40 41 /** 42 * Your MinStack object will be instantiated and called as such: 43 * MinStack obj = new MinStack(); 44 * obj.push(x); 45 * obj.pop(); 46 * int param_3 = obj.top(); 47 * int param_4 = obj.getMin(); 48 */
