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solution.ts
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solution.ts
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// #Medium #Top_100_Liked_Questions #Linked_List #Recursion #Data_Structure_II_Day_12_Linked_List
// #Udemy_Linked_List #Big_O_Time_O(n)_Space_O(1)
// #2023_08_29_Time_59_ms_(62.67%)_Space_44.7_MB_(26.03%)
/**
* Definition for singly-linked list.
* class ListNode {
* val: number
* next: ListNode | null
* constructor(val?: number, next?: ListNode | null) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
* }
*/
function swapPairs(head: ListNode | null): ListNode | null {
if (head === null) {
return null
}
const len = getLength(head)
return reverse(head, len)
}
function getLength(curr: ListNode | null): number {
let cnt = 0
while (curr !== null) {
cnt++
curr = curr.next
}
return cnt
}
// Recursive function to reverse in groups
function reverse(head: ListNode | null, len: number): ListNode | null {
// base case
if (len < 2) {
return head
}
let curr: ListNode | null = head
let prev: ListNode | null = null
let next: ListNode | null
for (let i = 0; i < 2; i++) {
// reverse linked list code
next = curr.next
curr.next = prev
prev = curr
curr = next
}
head.next = reverse(curr, len - 2)
return prev
}
export { swapPairs }