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merge-k-sorted-lists.js
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merge-k-sorted-lists.js
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// 23. Merge k Sorted Lists
// Hard
// Add to List
// Share
// Given an array of linked-lists lists, each linked list is sorted in ascending order.
// Merge all the linked-lists into one sort linked-list and return it.
// Example 1:
// Input: lists = [[1,4,5],[1,3,4],[2,6]]
// Output: [1,1,2,3,4,4,5,6]
// Explanation: The linked-lists are:
// [
// 1->4->5,
// 1->3->4,
// 2->6
// ]
// merging them into one sorted list:
// 1->1->2->3->4->4->5->6
// Example 2:
// Input: lists = []
// Output: []
// Example 3:
// Input: lists = [[]]
// Output: []
//brutal force method
/**
* Definition for singly-linked list.
* function ListNode(val, next) {
* this.val = (val===undefined ? 0 : val)
* this.next = (next===undefined ? null : next)
* }
*/
/**
* @param {ListNode[]} lists
* @return {ListNode}
*/
var mergeKLists = function(lists) {
const headOfLists = [];
let res = null;
let pointer = null;
lists.forEach((listHead, idx)=>{
headOfLists[idx] = listHead
})
// get through all the nodes
while (!checkAllNull(headOfLists)) {
const minIdx = getMinIdx(headOfLists);
// if not minIdx?
if (minIdx !== undefined) {
const curMinNode = new ListNode(headOfLists[minIdx].val)
//build new list
if (!res) {
res = curMinNode
pointer = res;
} else {
pointer.next = curMinNode;
pointer = pointer.next;
}
// move the header pointer
headOfLists[minIdx] = headOfLists[minIdx].next
}
}
return res;
};
function checkAllNull (arr) {
let res = true;
for (let i = 0; i < arr.length; i++) {
// while element is not null or undefined
if(arr[i]) {
res = false;
break;
}
}
return res;
}
function getMinIdx (arr) {
let minIdx;
for (let i = 0 ; i < arr.length; i++) {
const curNode = arr[i]
if(curNode) {
if (!minIdx) {
minIdx = [i]
} else if (curNode.val < arr[minIdx].val) {
minIdx = i
}
}
}
return minIdx;
}
// K 路归并算法 K-way merge
// Priority Queue