leetcode刷题记录——栈和队列
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题目
232.用栈实现队列
class MyQueue { private Stack<Integer> in = new Stack<>(); private Stack<Integer> out = new Stack<>(); public void push(int x) { in.push(x); } public int pop() { in2out(); return out.pop(); } public int peek() { in2out(); return out.peek(); } private void in2out() { if (out.isEmpty()) { while (!in.isEmpty()) { out.push(in.pop()); } } } public boolean empty() { return in.isEmpty() && out.isEmpty(); } }
225.用队列实现栈
class MyStack { private Queue<Integer> queue; public MyStack() { queue = new LinkedList<>(); } public void push(int x) { queue.add(x); int cnt = queue.size(); while (cnt-- > 1) { queue.add(queue.poll()); } } public int pop() { return queue.remove(); } public int top() { return queue.peek(); } public boolean empty() { return queue.isEmpty(); } }
155.最小栈
class MinStack { private Stack<Integer> dataStack; private Stack<Integer> minStack; private int min; public MinStack() { dataStack = new Stack<>(); minStack = new Stack<>(); min = Integer.MAX_VALUE; } public void push(int x) { dataStack.add(x); min = Math.min(min, x); minStack.add(min); } public void pop() { dataStack.pop(); minStack.pop(); min = minStack.isEmpty() ? Integer.MAX_VALUE : minStack.peek(); } public int top() { return dataStack.peek(); } public int getMin() { return minStack.peek(); } }
20.有效地括号
class Solution { public boolean isValid(String s) { Stack<Character> stack = new Stack<>(); for (char c : s.toCharArray()) { if (c == ‘(‘ || c == ‘{‘ || c == ‘[‘) { stack.push(c); } else { if (stack.isEmpty()) { return false; } char cStack = stack.pop(); boolean b1 = c == ‘)‘ && cStack != ‘(‘; boolean b2 = c == ‘]‘ && cStack != ‘[‘; boolean b3 = c == ‘}‘ && cStack != ‘{‘; if (b1 || b2 || b3) { return false; } } } return stack.isEmpty(); } }
739.每日温度
求数组中元素与下一个比它大元素之间的距离
class Solution { public int[] dailyTemperatures(int[] temperatures) { int n = temperatures.length; int[] dist = new int[n]; Stack<Integer> indexs = new Stack<>(); for (int curIndex = 0; curIndex < n; curIndex++) { while (!indexs.isEmpty() && temperatures[curIndex] > temperatures[indexs.peek()]) { int preIndex = indexs.pop(); dist[preIndex] = curIndex - preIndex; } indexs.add(curIndex); } return dist; } }
503.下一个更大的元素II
class Solution { public int[] nextGreaterElements(int[] nums) { int n = nums.length; int[] next = new int[n]; Arrays.fill(next, -1); Stack<Integer> pre = new Stack<>(); for (int i = 0; i < n * 2; i++) { int num = nums[i % n]; while (!pre.isEmpty() && nums[pre.peek()] < num) { next[pre.pop()] = num; } if (i < n){ pre.push(i); } } return next; } }
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