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155. min stack

admin 11月 15, 2020 0

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:

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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
 
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class  {

    
    private Stack<Integer> stack = new Stack<>();
   private Stack<Integer> minStack = new Stack<>();
    public () {
        
    }
    
    public void push(int x) {
        if (minStack.isEmpty() || x <= minStack.peek()) {
            minStack.push(x);
        }
        stack.push(x);
    }
    
    public void pop() {
        if (stack.peek().equals(minStack.peek())) {
            minStack.pop();
      }
        stack.pop();
    }
    
    public int top() {
        return stack.peek();
    }
    
    public int getMin() {
        return minStack.peek();
    }
}

/**
 * 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();
 */
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