Q155Min Stack.md

Q155Min Stack

Solution 1

Idea:

Build two stacks,one for function push ,pop,top ,and the other for getMin recording min elements in stack when push or pop.

Time Complexity:

O()

Space Complexity:

O()

Source code:

class MinStack {
    private Stack<Integer> stack = new Stack<Integer>();
    private Stack<Integer> minStack = new Stack<Integer>();
    
    public void push(int x) {
        stack.push(x);
        if(minStack.isEmpty() || x <= minStack.peek()){
        minStack.push(x);
        }
    }
    public void pop() {
        int x=minStack.peek();
        int y=stack.peek();
        if( y== x){  //sides of"=="can not be XXX.peak() simultaneously.
        minStack.pop();
        }
        stack.pop();
    }
    public int top() {
        return stack.peek();
    }
    public int getMin() {
        return minStack.peek();
    }
}

Reference:

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