https://leetcode.com/problems/min-stack/
Implement a stack so that it can perform top, pop, push operations, while also being able to return the current minimum value
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Input
-----------------
["MinStack", "push", "push", "push", "getMin", "pop", "top", "getMin"]
[[], [-2], [0], [-3] , [], [], [], []]
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Output
----------------
[null, null, null, null, -3, null, 0, -2]
Explanation
MinStack minStack = new MinStack ();
minStack.push (-2);
minStack.push (0);
minStack.push (-3) ;
minStack.getMin (); // return -3
minStack.pop ();
minStack.top (); // return 0
minStack.getMin ();// return -2
analysis:
Set two stacks, one to save the inserted value and one to save the minimum value of the current element after insertion
1. Implement a stack with a linked list
class MinStack {
public:
/** initialize your data structure here. */
struct StackNode{
int val;
StackNode* next;
StackNode(int val){
this->val = val;
}
};
StackNode* top_stack;
StackNode* min_stack;
MinStack(){
top_stack=NULL;
min_stack=NULL;
}
void push(int x) {
if(!top_stack || x <= min_stack->val)
{
StackNode* temp1 = new StackNode(x);
temp1->next = min_stack;
min_stack = temp1;
}
StackNode* temp = new StackNode(x);
temp->next = top_stack;
top_stack = temp;
}
void pop() {
if(!top_stack)
return;
if(top_stack->val == min_stack->val)
{
StackNode* temp = min_stack;
min_stack = min_stack->next;
delete temp;
}
StackNode* temp1 = top_stack;
top_stack = top_stack->next;
delete temp1;
}
int top() {
return top_stack->val;
}
int getMin() {
return min_stack->val;
}
};
/**
* Your MinStack object will be instantiated and called as such:
* MinStack* obj = new MinStack();
* obj->push(x);
* obj->pop();
* int param_3 = obj->top();
* int param_4 = obj->getMin();
*/
2. Use the built-in vector
class MinStack {
public:
/** initialize your data structure here. */
vector<int> top_stack;
vector<int> min_stack;
void push(int x) {
if(top_stack.empty() || x <= min_stack.back())
{
top_stack.push_back(x);
min_stack.push_back(x);
}
else
{
top_stack.push_back(x);
}
}
void pop() {
if(top_stack.back() == min_stack.back())
{
top_stack.pop_back();
min_stack.pop_back();
}
else
top_stack.pop_back();
}
int top() {
return top_stack.back();
}
int getMin() {
return min_stack.back();
}
};
/**
* Your MinStack object will be instantiated and called as such:
* MinStack* obj = new MinStack();
* obj->push(x);
* obj->pop();
* int param_3 = obj->top();
* int param_4 = obj->getMin();
*/