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.
class MinStack {
private LinkedList<Node> stack = new LinkedList<>();
/* value, min
-3, -3
0, -2
-2, -2
*/
/** initialize your data structure here. */
public MinStack() {
}
public void push(int x) {
Node node;
if (stack.isEmpty()) {
node = new Node(x, x);
} else {
int min = Math.min(x, stack.peekFirst().min);
node = new Node(x, min);
}
stack.push(node);
System.out.printf("val %d min %d\n", node.value, node.min);
}
public void pop() {
Node pop = stack.pop();
System.out.printf("pop val %d min %d\n", pop.value, pop.min);
}
public int top() {
return stack.peekFirst().value;
}
public int getMin() {
Node first = stack.peekFirst();
System.out.printf("getMin val %d min %d\n", first.value, first.min);
return first.min;
}
class Node {
Node(int value, int min) {
this.value= value;
this.min = min;
}
int value;
int min;
}
}
/**
* 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();
*/