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Merge pull request #430 from taekwon-dev/main
[์œคํƒœ๊ถŒ] Week4 ๋ฌธ์ œ ํ’€์ด
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โ€Žmissing-number/taekwon-dev.java

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/**
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* ์‹œ๊ฐ„ ๋ณต์žก๋„: O(n)
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* - ๊ณต์ฐจ๊ฐ€ 1์ธ ๋“ฑ์ฐจ์ˆ˜์—ด, ๋“ฑ์ฐจ์ˆ˜์—ด์˜ ํ•ฉ ๊ณต์‹ ํ™œ์šฉํ•˜์—ฌ ๊ธฐ๋Œ€ ๊ฐ’์„ ๊ณ„์‚ฐ -> O(1)
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* - ์ฃผ์–ด์ง„ ๋ฐฐ์—ด์„ ์ˆœํšŒํ•˜๋ฉด์„œ ๊ฐ ์›์†Œ์˜ ํ•ฉ์„ ๊ณ„์‚ฐ -> O(n)
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* - ๊ธฐ๋Œ€ ๊ฐ’์—์„œ ์‹ค์ œ ๊ฐ ์›์†Œ์˜ ํ•ฉ์„ ๋นผ๋ฉด ์ •๋‹ต -> O(1)
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*
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* ๊ณต๊ฐ„ ๋ณต์žก๋„: O(1)
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*
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*/
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class Solution {
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public int missingNumber(int[] nums) {
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int len = nums.length;
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int expectedSum = len * (len + 1) / 2;
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int actualSum = 0;
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for (int num: nums) {
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actualSum += num;
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}
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return expectedSum - actualSum;
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}
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}

โ€Žvalid-palindrome/taekwon-dev.java

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/**
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* ์‹œ๊ฐ„ ๋ณต์žก๋„: O(n)
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* - ์ •๊ทœ์‹์„ ํ†ตํ•ด Alphanumeric ๋งŒ ๋‚จ๊ธฐ๊ธฐ. -> O(n)
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* - ์†Œ๋ฌธ์ž๋กœ ๋ณ€ํ™˜ -> O(n)
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* - ํˆฌ ํฌ์ธํ„ฐ๋ฅผ ์ด์šฉํ•˜๊ธฐ ๋•Œ๋ฌธ์— -> O(n/2)
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* ๊ณต๊ฐ„ ๋ณต์žก๋„: O(n)
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*/
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class Solution {
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public boolean isPalindrome(String s) {
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s = s.replaceAll("[^a-zA-Z0-9]", "").toLowerCase();
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char[] c = s.toCharArray();
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int left = 0;
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int right = c.length - 1;
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while (left < right) {
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if (c[left++] != c[right--]) {
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return false;
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}
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}
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return true;
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}
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}

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