LeetCode155. 最小栈(java)
题目:
设计一个支持 push,pop,top 操作,并能在常数时间内检索到最小元素的栈。
push(x) – 将元素 x 推入栈中。
pop() – 删除栈顶的元素。
top() – 获取栈顶元素。
getMin() – 检索栈中的最小元素。
示例:
代码:
- 解法一
class MinStack {
private Stack<Integer> stackData;
private Stack<Integer> stackMin;
/** 构造方法 */
public MinStack() {
stackData = new Stack<Integer>();
stackMin = new Stack<Integer>();
}
/*将元素x推入栈中*/
public void push(int x) {
if(stackMin.empty()) {
stackMin.push(x);
} else if(x <= getMin()) {
stackMin.push(x);
} else {
int newMin = getMin();
stackMin.push(newMin);
}
stackData.push(x);
}
/*删除栈顶元素*/
public void pop() {
if(stackData.empty()) {
throw new RuntimeException("your stack is empty!");
}
stackMin.pop();
stackData.pop();
}
/*获取栈顶元素*/
public int top() {
if(stackData.empty()) {
throw new RuntimeException("your stack is empty!");
}
return stackData.peek();
}
/*检索栈中的最小元素*/
public int getMin() {
if(stackMin.empty()) {
throw new RuntimeException("your stack is empty!");
}
return stackMin.peek();
}
}
- 解法二
class MinStack {
// 支持push,pop,top的栈
private Stack<Integer> mainStack;
// 支持在常数时间内检索到最小元素的单调栈
private Stack<Integer> minStack;
/** initialize your data structure here. */
public MinStack() {
this.mainStack = new Stack<>();
this.minStack = new Stack<>();
}
public void push(int x) {
mainStack.push(x);
// 实际上每次push只需要记录更小的值
if(minStack.isEmpty() || minStack.peek() >= x)
minStack.push(x);
}
//弹栈
public void pop() {
int tmp = mainStack.pop();
if(tmp == minStack.peek())
minStack.pop();
}
//获取栈顶元素
public int top() {
return mainStack.peek();
}
//获取最小元素
public int getMin() {
return minStack.peek();
}
}
- 别人的代码
class MinStack {
private Deque<Integer> mainStack; // 主栈,存储所有数据
private Deque<Integer> minStack; // 将数据压入主栈时,存储最小值
/** initialize your data structure here. */
public MinStack() {
mainStack = new ArrayDeque<>();
minStack = new ArrayDeque<>();
}
public void push(int x) {
mainStack.push(x);
Integer min = minStack.peek();
if (min == null || x <= min) {
minStack.push(x);
}
}
public int pop() {
int cur = mainStack.pop();
if (cur == minStack.peek()) {
minStack.pop();
}
return cur;
}
public int top() {
return mainStack.peek();
}
public int getMin() {
return minStack.peek();
}
}