leetcode 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.

解决方案:

可以看到STL的解决方案跟大多数的c语言解决方案还是有差距的,后序我找一找基于链表的整齐点的c语言实现

The key idea is use a another stack to store the minimum value of the corresponding stack. Put differently, min[i] equals the minimum element where data[i] is the top of this sub-stack.

We can use a full size of min where it’s size equals the data’s, but it’s not necessary.

I have 2 main concerns about the algorithm:

1 We should pop the element in min IFF there’s match of data.top().

2 If we have multiple minima, for example [0, 1, 0] in data, then the min should be [0, 0]. Otherwise, the the pop operation wouldn’t work properly. As a result, we should push the element if x <= min.top().

class MinStack {
public:
    void push(int x) {
        s.push(x);
        if (mins.empty() || x<=mins.top()) {
            mins.push(x);
        }
    }

    void pop() {
        int temp = s.top();
        s.pop();
        if (temp == mins.top()) {
            mins.pop();
        }
    }

    int top() {
        return s.top();
    }

    int getMin() {
        return mins.top();
    }

private:
    stack<int> s;
    stack<int> mins;
};

STL list实现:

class MinStack {
    private:
        list<int> s;
        int min;


    public:

        MinStack()
        {
            min=INT_MAX;
        }

        void push(int x) {
            if(x<min) min=x;
            s.push_back(x);

        }

        void pop() {
            if(s.back()==min)
            {
                s.pop_back();
                min=INT_MAX;
                list<int>::iterator it=s.begin();
                while(it!=s.end())
                {
                    if(*it<min) min=*it;
                    it++;
                }
            }else
                s.pop_back();
        }

        int top() {
            return s.back();
        }

        int getMin() {
            return min;
        }
    };

python解决方案:

class MinStack:
# @param x, an integer
def __init__(self):
    # the stack it self
    self.A = []
    self.minS=[]
# @return an integer
def push(self, x):
    n=len(self.A)
    if n==0:
        self.minS.append(x)
    else:
        lastmin=self.minS[-1]
        if x<=lastmin:
            self.minS.append(x)
    self.A.append(x)
# @return nothing
def pop(self):
    if len(self.A)>0 and self.A.pop()==self.minS[-1]:
        self.minS.pop()
# @return an integer
def top(self):
    return self.A[-1]


# @return an integer
def getMin(self):
    return self.minS[-1]

python解决方案2:

class MinStack:

def __init__(self):
    self.q = []

# @param x, an integer
# @return an integer
def push(self, x):
    curMin = self.getMin()
    if curMin == None or x < curMin:
        curMin = x
    self.q.append((x, curMin));

# @return nothing
def pop(self):
    self.q.pop()


# @return an integer
def top(self):
    if len(self.q) == 0:
        return None
    else:
        return self.q[len(self.q) - 1][0]


# @return an integer
def getMin(self):
    if len(self.q) == 0:
        return None
    else:
        return self.q[len(self.q) - 1][1]

  asked Apr 14  in Min Stack  by  charles8135 (180 points)    

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