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Copy path155_Min_Stack.java
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72 lines (60 loc) · 1.64 KB
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/*
* 155. Min Stack
* Target: 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.
* Difficulty：Easy
* Classification：Stack, Design
*/
/*
* Solution 1
* 2019-08-27 Runtime: 47 ms
* Algorithm: => Stack. Every time put the Node and calculate the minimum value of stack.
* Time Complexity: O(n). Space Conplexity: O(1)
*/
class MinStack {
private Node head;
/** initialize your data structure here. */
public MinStack() {
}
public void push(int x) {
if (head == null) {
head = new Node(x, x);
} else {
head = new Node(x, Math.min(head.min, x), head);
}
}
public void pop() {
head = head.next;
}
public int top() {
return head.val;
}
public int getMin() {
return head.min;
}
private class Node {
int val, min;
Node next;
private Node(int val, int min) {
this.val = val;
this.min = min;
this.next = null;
}
private Node(int val, int min, Node next) {
this.val = val;
this.min = min;
this.next = next;
}
}
}
/**
* 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();
*/