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[se6816] WEEK 11 solutions #2298

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Merged
se6816 merged 3 commits into from
Jan 25, 2026
Merged

[se6816] WEEK 11 solutions #2298

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788967c
missing number
se6816 Jan 24, 2026
6efb604
merge intervals
se6816 Jan 24, 2026
f3f44e4
reorder list
se6816 Jan 24, 2026
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26 changes: 26 additions & 0 deletions merge-intervals/se6816.java
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/**
탐욕법을 이용하여, 연산하는 방식
*/
class Solution {
public int[][] merge(int[][] intervals) {

Arrays.sort(intervals, (a,b) -> a[0] - b[0]);

List<int[]> result = new ArrayList<>();
int startNum = intervals[0][0];
int endNum = intervals[0][1];
for(int i = 1; i < intervals.length; i++) {
if(endNum >= intervals[i][0]) {
endNum = Math.max(endNum, intervals[i][1]);
continue;
}

result.add(new int[]{startNum, endNum});
startNum = intervals[i][0];
endNum = intervals[i][1];
}
result.add(new int[]{startNum, endNum});

return result.toArray(new int[result.size()][]);
}
}
27 changes: 27 additions & 0 deletions missing-number/se6816.java
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/**
최댓값을 기준으로 배열의 합과 1~N까지의 합을 비교하여 확인하는 방식
*/
class Solution {
public int missingNumber(int[] nums) {
int max = 0;
int sum = 0;
boolean existsZero = false;
for(int i = 0; i < nums.length; i++) {
max = Math.max(nums[i], max);
sum += nums[i];
if(nums[i] == 0){
existsZero = true;
}
}

int result = (max * (max + 1)) / 2 - sum;

if(!existsZero) {
result = 0;
} else if(result == 0) {
result = max + 1;
}

return result;
}
}
25 changes: 25 additions & 0 deletions reorder-list/se6816.java
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class Solution {
public void reorderList(ListNode head) {
if(head.next == null) return;

ListNode prev = null;
while (true) {
ListNode tail = head;
while (tail.next != null) {
prev = tail;
tail = tail.next;
}

if (prev == head) break;

// tail 이동
ListNode headNext = head.next;
prev.next = null;
head.next = tail;
tail.next = headNext;

head = headNext;
}
}
}