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package leetcode_study
import io.kotest.matchers.shouldBe
import org.junit.jupiter.api.Test
/**
* Leetcode
* 15. 3Sum
* Medium
*/
class `3Sum` {
/**
* 3์ค for๋ฌธ์ผ๋ก ํ์ด๋ดค๋๋ฐ ์๊ฐ ์ด๊ณผ๊ฐ ๋๋๋ผ๊ณ ์(๋น์ฐ)
* ์ฌ์ค ์ ๋ชจ๋ฅด๊ฒ ์ด์ Topic๊ณผ ํํธ๋ฅผ ์ด์ง ๋ดค๋๋ฐ ํฌ ํฌ์ธํฐ๊ฐ ์๊ธธ๋ ์ด๊ฑธ ์ด์ฉํด์ ํ์ด๋ณด๊ธฐ๋ก ํ์ต๋๋ค!
*
* Runtime: 72 ms(Beats: 60.54 %)
* Time Complexity: O(n^2)
*
* Memory: 56.28 MB(Beats: 49.51 %)
* Space Complexity: O(n^2)
*/
fun threeSum(nums: IntArray): List<List<Int>> {
val answer = mutableListOf<List<Int>>()
// ๋ฐฐ์ด ์ ๋ ฌ - ์ค๋ณต๋ ๊ฒฝ์ฐ๋ฅผ ์ ๊ฑฐํ๊ณ ํจ์จ์ ์ผ๋ก ํ์ํ๊ธฐ ์ํ์ฌ
nums.sort()
// nums[i]์ ์ด์ ๊ฐ์ ์๋ฏธํฉ๋๋ค.
var prev = Integer.MIN_VALUE
for (i in nums.indices) {
// ์ด์ ๊ฐ๊ณผ ๋์ผํ ๊ฐ์ด๋ผ๋ฉด ์คํตํ์ฌ ์ค๋ณต๋ ๊ฒฝ์ฐ๋ฅผ ์ ๊ฑฐํฉ๋๋ค.
if (nums[i] == prev) {
continue
}
// ํฌ ํฌ์ธํฐ ์๊ณ ๋ฆฌ์ฆ์ ์ด์ฉํ์ฌ ๋ค ๋ํ์ฌ 0์ด ๋๋ ๊ฒฝ์ฐ์ ์๋ฅผ ์ฐพ์ต๋๋ค.
var left = i + 1
var right = nums.size - 1
while (left < right) {
if (nums[i] + nums[left] + nums[right] > 0) { // ํฉ์ด 0๋ณด๋ค ํฌ๋ค๋ฉด right๋ฅผ ์ค์
๋๋ค.
// if ๋ด์ ์๋ while๋ฌธ๋ค์ ์ค๋ณต ๊ฒฝ์ฐ์ ์๋ฅผ ํผํ๊ธฐ ์ํจ์
๋๋ค.
while (0 <= right - 1 && nums[right - 1] == nums[right]) {
right--
}
right--
} else if (nums[i] + nums[left] + nums[right] < 0) { // ํฉ์ด 0๋ณด๋ค ์ ๋ค๋ฉด left๋ฅผ ๋์
๋๋ค.
while (left + 1 <= nums.size - 1 && nums[left] == nums[left + 1]) {
left++
}
left++
} else { // ํฉ์ด 0์ด๋ผ๋ฉด ๊ฒฝ์ฐ์ ์๋ฅผ ์ถ๊ฐํฉ๋๋ค.
answer.add(listOf(nums[i], nums[left], nums[right]))
while (left + 1 <= nums.size - 1 && nums[left] == nums[left + 1]) {
left++
}
left++
while (0 <= right - 1 && nums[right - 1] == nums[right]) {
right--
}
right--
}
}
prev = nums[i]
}
return answer
}
/**
* ์๊ฐ ๋ณต์ก๋๋ ๊ณต๊ฐ ๋ณต์ก๋๊ฐ ๊ฐ์ ๋์ง ์์์ง๋ง ๊ฐ๋
์ฑ ์ธก๋ฉด์์ ๊ฐ์ ํด๋ณธ ๋ฒ์ ์
๋๋ค.
* Runtime: 66 ms(Beats: 65.59 %)
* Time Complexity: O(n^2)
*
* Memory: 56.64 MB(Beats: 43.12 %)
* Space Complexity: O(n^2)
*/
fun threeSum2(nums: IntArray): List<List<Int>> {
val answer = mutableListOf<List<Int>>()
nums.sort()
// ์ฒซ ์ธ ์์ ํฉ์ด 0๋ณด๋ค ํฌ๊ฑฐ๋, ๋ง์ง๋ง ์ธ ์์ ํฉ์ด 0๋ณด๋ค ์์ผ๋ฉด ๋ถ๊ฐ๋ฅ
val lastIndex = nums.size - 1
if (nums[0] + nums[1] + nums[2] > 0 ||
nums[lastIndex] + nums[lastIndex - 1] + nums[lastIndex - 2] < 0
) {
return emptyList()
}
var prev = nums[0] - 1
for (i in nums.indices) {
// ์กฐ๊ธฐ ์ข
๋ฃ ์กฐ๊ฑด ์ถ๊ฐ
if (nums[i] > 0) {
break
}
if (nums[i] == prev) {
continue
}
var left = i + 1
var right = nums.size - 1
while (left < right) {
// ์ค๋ณต ๋ก์ง ์ ๊ฑฐ ๋ฐ sum ๋ณ์ํ
val sum = nums[i] + nums[left] + nums[right]
when {
sum > 0 -> right = skipDuplicates(nums, right, false)
sum < 0 -> left = skipDuplicates(nums, left, true)
else -> {
answer.add(listOf(nums[i], nums[left], nums[right]))
left = skipDuplicates(nums, left, true)
right = skipDuplicates(nums, right, false)
}
}
}
prev = nums[i]
}
return answer
}
private fun skipDuplicates(nums: IntArray, index: Int, isLeft: Boolean): Int {
var current = index
return if (isLeft) {
while (current + 1 < nums.size && nums[current] == nums[current + 1]) current++
current + 1
} else {
while (0 <= current - 1 && nums[current - 1] == nums[current]) current--
current - 1
}
}
@Test
fun test() {
threeSum(intArrayOf(-1, 0, 1, 2, -1, -4)) shouldBe listOf(
listOf(-1, -1, 2),
listOf(-1, 0, 1)
)
threeSum(intArrayOf(0, 1, 1)) shouldBe emptyList<Int>()
threeSum(intArrayOf(0, 0, 0)) shouldBe listOf(
listOf(0, 0, 0)
)
threeSum(intArrayOf(-2, 0, 0, 2, 2)) shouldBe listOf(
listOf(-2, 0, 2)
)
threeSum2(intArrayOf(-1, 0, 1, 2, -1, -4)) shouldBe listOf(
listOf(-1, -1, 2),
listOf(-1, 0, 1)
)
threeSum2(intArrayOf(0, 1, 1)) shouldBe emptyList<Int>()
threeSum2(intArrayOf(0, 0, 0)) shouldBe listOf(
listOf(0, 0, 0)
)
threeSum2(intArrayOf(-2, 0, 0, 2, 2)) shouldBe listOf(
listOf(-2, 0, 2)
)
}
}