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MaxStack.java
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MaxStack.java
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/*
* Title: Max Stack
*
* Implement a LIFO stack that has a push(), pop(), and max() function, where
* max() returns the maximum value in the stack. All of these functions should
* run in O(1) time.
*
* Execution: javac MaxStack.java && java MaxStack
*
* For more details, check out http://www.byte-by-byte.com/maxstack/
*/
public class MaxStack {
private class Node {
private int value;
private Node next;
private Node oldMax;
}
private Node stack;
private Node max;
public MaxStack() {}
public void push(int x) {
Node n = new Node();
n.value = x;
if (stack == null) {
stack = n;
} else {
n.next = stack;
stack = n;
}
if (max == null || n.value > max.value) {
n.oldMax = max;
max = n;
}
}
public int pop() {
if (stack == null) {
throw new NullPointerException("Stack is Null");
}
Node n = stack;
stack = n.next;
max = n.oldMax;
return n.value;
}
public int max() {
if (max == null) {
throw new NullPointerException("Max is Null");
}
return max.value;
}
public static void test_1() {
MaxStack s = new MaxStack();
s.push(1);
s.push(100);
s.push(5);
assert s.max() == 100;
}
public static void test_2() {
MaxStack s = new MaxStack();
s.push(1);
s.push(2);
s.push(3);
assert s.max() == 3;
}
public static void test_3() {
MaxStack s = new MaxStack();
s.push(-1);
s.push(2);
s.push(-3);
assert s.max() == 2;
}
// Sample test cases
public static void main(String[] args) {
test_1();
test_2();
test_3();
System.out.println("Passed all test cases");
}
}