LeetCode – Refresh – Min Stack

Use two stacks :

class MinStack {
private:
stack<int> s, minS;
public:
void push(int x) {
if (minS.empty() || x <= minS.top()) {
minS.push(x);
}
s.push(x);
}

void pop() {
if (minS.top() == s.top()) {
minS.pop();
}
s.pop();
}

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

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

A fancy algorithm, just use one stack and a number. But it will failed with INT_MIN and INT_MAX as overflow.

class MinStack {
private:
int minValue;
stack<int> s;
public:
void push(int x) {
if (s.empty()) {
minValue = x;
s.push(x);
} else if (x < minValue) {
s.push(2*x - minValue);
minValue = x;
} else {
s.push(x);
}
}

void pop() {
if (s.top() < minValue) {
minValue = 2*minValue - s.top();
}
s.pop();
}

int top() {
if (s.top() < minValue) {
return 2*minValue - s.top();
}
return s.top();
}

int getMin() {
return minValue;
}
};