Problem
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.
My Solution
class MinStack {
public int[] data;
public int min = Integer.MAX_VALUE;
public int top = -1;
/** initialize your data structure here. */
public MinStack() {
data = new int[10000];
}
public void push(int x) {
if (x < min) {
min = x;
}
++top;
if (top < data.length - 1) {
data[top] = x;
}
}
public void pop() {
if (top >= 0) {
top--;
}
int t = top;
min = Integer.MAX_VALUE;
while (t != -1) {
if (data[t] < min) {
min = data[t];
}
t--;
}
}
public int top() {
if (top >= 0 && top <= data.length - 1) {
return data[top];
} else {
return 0;
}
}
public int getMin() {
return min;
}
}
Great Solution
public class MinStack {
long min;
Stack<Long> stack;
public MinStack(){
stack=new Stack<>();
}
public void push(int x) {
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;
}
}
public void pop() {
if (stack.isEmpty()) return;
long pop=stack.pop();
if (pop<0) min=min-pop;//If negative, increase the min value
}
public int top() {
long top=stack.peek();
if (top>0){
return (int)(top+min);
}else{
return (int)(min);
}
}
public int getMin() {
return (int)min;
}
}
