leetcode-java/src/MinStack.java at master · fluency03/leetcode-java · GitHub

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/**
 * 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.
 *
 */


importjava.util.SortedMap;
importjava.util.TreeMap;


classMinStack {
SortedMap<Integer, Integer> map = newTreeMap<>();;
Stack<Integer> st = newStack<>();

/** initialize your data structure here. */
publicMinStack() { }

publicvoidpush(intx) {
if (map.containsKey(x)) {
map.put(x, map.get(x)+1);
 } else {
map.put(x, 1);
 }

st.push(x);
 }

publicvoidpop() {
IntegertopEle = st.peek();
intcount = map.get(topEle);
count--;
if (count <= 0) {
map.remove(topEle);
 } else {
map.put(topEle, count);
 }

st.pop();
 }

publicinttop() {
returnst.peek();
 }

publicintgetMin() {
returnmap.firstKey();
 }
}


/**
 * https://discuss.leetcode.com/topic/4953/share-my-java-solution-with-only-one-stack
 */
classMinStack2 {
staticclassElement
 {
finalintvalue;
finalintmin;
Element(finalintvalue, finalintmin)
 {
this.value = value;
this.min = min;
 }
 }
finalStack<Element> stack = newStack<>();

publicvoidpush(intx) {
finalintmin = (stack.empty()) ? x : Math.min(stack.peek().min, x);
stack.push(newElement(x, min));
 }

publicvoidpop()
 {
stack.pop();
 }

publicinttop()
 {
returnstack.peek().value;
 }

publicintgetMin()
 {
returnstack.peek().min;
 }
}


/**
 * https://discuss.leetcode.com/topic/4953/share-my-java-solution-with-only-one-stack
 */
classMinStack3 {
longmin;
Stack<Long> stack;

publicMinStack(){
stack=newStack<>();
 }

publicvoidpush(intx) {
if (stack.isEmpty()){
stack.push(0L);
min=x;
 }else{
stack.push(x-min);//Could be negative if min value needs to change
if (x<min) min=x;
 }
 }

publicvoidpop() {
if (stack.isEmpty()) return;

longpop=stack.pop();

if (pop<0) min=min-pop;//If negative, increase the min value

 }

publicinttop() {
longtop=stack.peek();
if (top>0){
return (int)(top+min);
 }else{
return (int)(min);
 }
 }

publicintgetMin() {
return (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();
 */