Created
March 30, 2019 14:51
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155. Min Stack | |
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. | |
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; | |
} | |
} |
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