Fusionar dos listas ordenadas

Lectura

Fusionar dos listas ordenadas (Java, Python, PHP, Javascript, C++)

Dadas dos listas enlazadas, combine ambas en una sola lista ordenada, y devuelva el puntero de inicio de la lista fusionada.

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Código de la solución

Java

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode dummy = new ListNode(0);
        ListNode current = dummy;

        while (list1 != null && list2 != null) {
            if (list1.val <= list2.val) {
                current.next = list1;
                list1 = list1.next;
            } else {
                current.next = list2;
                list2 = list2.next;
            }
            current = current.next;
        }

        if (list1 != null) {
            current.next = list1;
        } else {
            current.next = list2;
        }

        return dummy.next;
    }
}

Python

class Solution(object):
    def mergeTwoLists(self, list1, list2):
        dummy = ListNode(0)
        current = dummy

        while list1 and list2:
            if list1.val <= list2.val:
                current.next = list1
                list1 = list1.next
            else:
                current.next = list2
                list2 = list2.next
            current = current.next

        if list1:
            current.next = list1
        else:
            current.next = list2

        return dummy.next

PHP

class Solution {

    /**
     * @param ListNode $list1
     * @param ListNode $list2
     * @return ListNode
     */
    function mergeTwoLists($list1, $list2) {
        $dummy = new ListNode(0);
        $current = $dummy;

        while ($list1 !== null && $list2 !== null) {
            if ($list1->val <= $list2->val) {
                $current->next = $list1;
                $list1 = $list1->next;
            } else {
                $current->next = $list2;
                $list2 = $list2->next;
            }
            $current = $current->next;
        }

        if ($list1 !== null) {
            $current->next = $list1;
        } else {
            $current->next = $list2;
        }

        return $dummy->next;
    }
}

JavaScript

/**
 * @param {ListNode} list1
 * @param {ListNode} list2
 * @return {ListNode}
 */
var mergeTwoLists = function(list1, list2) {
    let dummy = new ListNode(0);
    let current = dummy;

    while (list1 !== null && list2 !== null) {
        if (list1.val <= list2.val) {
            current.next = list1;
            list1 = list1.next;
        } else {
            current.next = list2;
            list2 = list2.next;
        }
        current = current.next;
    }

    if (list1 !== null) {
        current.next = list1;
    } else {
        current.next = list2;
    }

    return dummy.next;
};

C++

class Solution {
public:
    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
        ListNode dummy(0);
        ListNode* current = &dummy;

        while (list1 != nullptr && list2 != nullptr) {
            if (list1->val <= list2->val) {
                current->next = list1;
                list1 = list1->next;
            } else {
                current->next = list2;
                list2 = list2->next;
            }
            current = current->next;
        }

        if (list1 != nullptr) {
            current->next = list1;
        } else {
            current->next = list2;
        }

        return dummy.next;
    }
};