59 preguntas de la entrevista - cola máxima II.
//没看懂题....
class MaxQueue {
private Deque<Integer> queue;
private Deque<Integer> help;
public MaxQueue() {
queue = new ArrayDeque<>();
help = new ArrayDeque<>();
}
public int max_value() {
return queue.isEmpty() ? -1 : help.peek();
}
public void push_back(int value) {
queue.offer(value);
while(!help.isEmpty() && value > help.peekLast()) {
help.pollLast();
}
help.offer(value);
}
public int pop_front() {
if(queue.isEmpty()) {
return -1;
}
int val = queue.pop();
if(help.peek() == val) {
help.pop();
}
return val;
}
}
234. Lista palíndromo
class Solution {
public boolean isPalindrome(ListNode head) {
List<Integer> vals = new ArrayList<>();
ListNode currentNode = head;
while (currentNode != null) {
vals.add(currentNode.val);
currentNode = currentNode.next;
}
int front = 0;
int back = vals.size() - 1;
while (front < back) {
if (!vals.get(front).equals(vals.get(back))) {
return false;
}
front++;
back--;
}
return true;
}
}
//递归
class Solution {
private ListNode frontPointer;
private boolean recursivelyCheck(ListNode currentNode) {
if (currentNode != null) {
if (!recursivelyCheck(currentNode.next)) return false;
if (currentNode.val != frontPointer.val) return false;
frontPointer = frontPointer.next;
}
return true;
}
public boolean isPalindrome(ListNode head) {
frontPointer = head;
return recursivelyCheck(head);
}
}
class Solution {
public boolean isPalindrome(ListNode head) {
// 要实现 O(n) 的时间复杂度和 O(1) 的空间复杂度,需要翻转后半部分
if (head == null || head.next == null) {
return true;
}
ListNode fast = head;
ListNode slow = head;
// 根据快慢指针,找到链表的中点
while(fast.next != null && fast.next.next != null) {
fast = fast.next.next;
slow = slow.next;
}
slow = reverse(slow.next);
while(slow != null) {
if (head.val != slow.val) {
return false;
}
head = head.next;
slow = slow.next;
}
return true;
}
private ListNode reverse(ListNode head){
// 递归到最后一个节点,返回新的新的头结点
if (head.next == null) {
return head;
}
ListNode newHead = reverse(head.next);
head.next.next = head;
head.next = null;
return newHead;
}
}
189. matriz rotativa
class Solution {
public void rotate(int[] nums, int k) {
int temp, previous;
for (int i = 0; i < k; i++) {
previous = nums[nums.length - 1];
for (int j = 0; j < nums.length; j++) {
temp = nums[j];
nums[j] = previous;
previous = temp;
}
}
}
}
class Solution {
public void rotate(int[] nums, int k) {
int[] a = new int[nums.length];
for (int i = 0; i < nums.length; i++) {
a[(i + k) % nums.length] = nums[i];
}
for (int i = 0; i < nums.length; i++) {
nums[i] = a[i];
}
}
}
class Solution {
public void rotate(int[] nums, int k) {
k = k % nums.length;
int count = 0;
for (int start = 0; count < nums.length; start++) {
int current = start;
int prev = nums[start];
do {
int next = (current + k) % nums.length;
int temp = nums[next];
nums[next] = prev;
prev = temp;
current = next;
count++;
} while (start != current);
}
}
}
class Solution {
public void rotate(int[] nums, int k) {
k %= nums.length;
reverse(nums, 0, nums.length - 1);
reverse(nums, 0, k - 1);
reverse(nums, k, nums.length - 1);
}
public void reverse(int[] nums, int start, int end) {
while (start < end) {
int temp = nums[start];
nums[start] = nums[end];
nums[end] = temp;
start++;
end--;
}
}
}
Cuanto más se sabe, más usted no sabe.
Forma correcta sin necesidad de cirugía, los pacientes aún pueden buscar, no hay ninguna manera de la cirugía, poniendo fin a la cirugía.
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