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Solution.cpp
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Solution.cpp
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// #Easy #Top_100_Liked_Questions #Two_Pointers #Stack #Linked_List #Recursion
// #Level_2_Day_3_Linked_List #Udemy_Linked_List #Big_O_Time_O(n)_Space_O(1)
// #2024_05_24_Time_154_ms_(83.63%)_Space_116.7_MB_(68.62%)
/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode() : val(0), next(nullptr) {}
* ListNode(int x) : val(x), next(nullptr) {}
* ListNode(int x, ListNode *next) : val(x), next(next) {}
* };
*/
class Solution {
public:
bool isPalindrome(ListNode* head) {
int len = 0;
ListNode* right = head;
// Calculate the length
while (right != nullptr) {
right = right->next;
len++;
}
// Reverse the right half of the list
len = len / 2;
right = head;
for (int i = 0; i < len; i++) {
right = right->next;
}
ListNode* prev = nullptr;
while (right != nullptr) {
ListNode* next = right->next;
right->next = prev;
prev = right;
right = next;
}
// Compare left half and right half
for (int i = 0; i < len; i++) {
if (prev != nullptr && head->val == prev->val) {
head = head->next;
prev = prev->next;
} else {
return false;
}
}
return true;
}
};