LIS 추가

Author: jdalma

longest-increasing-subsequence/jdalma.md

@@ -0,0 +1,72 @@
+package leetcode_study
+
+import io.kotest.matchers.shouldBe
+import org.junit.jupiter.api.Test
+
+class `longest-increasing-subsequence` {
+
+    fun lengthOfLIS(nums: IntArray): Int {
+        return usingBinarySearch(nums)
+    }
+
+    /**
+     * 이전 최장 수열 길이를 재사용한다.
+     * TC: O(n^2), SC: O(n)
+     */
+    private fun usingDP(nums: IntArray): Int {
+        val dp = IntArray(nums.size) { 1 }
+
+        for (i in 1 until nums.size) {
+            for (j in 0 until i) {
+                if (nums[i] > nums[j] && dp[i] < dp[j] + 1) {
+                    dp[i] = dp[j] + 1
+                }
+            }
+        }
+
+        return dp.max()
+    }
+
+    /**
+     * 최장 수열을 직접 갱신한다.
+     * TC: O(n * log n), SC: O(n)
+     */
+    private fun usingBinarySearch(nums: IntArray): Int {
+
+        fun binarySearch(list: List<Int>, number: Int): Int {
+            var (low, high) = 0 to list.size - 1
+
+            while (low <= high) {
+                val mid = (low + high) / 2
+                if (list[mid] == number) {
+                    return mid
+                } else if (list[mid] < number) {
+                    low = mid + 1
+                } else {
+                    high = mid - 1
+                }
+            }
+            return low
+        }
+
+        val result = mutableListOf<Int>()
+
+        for (num in nums) {
+            if (result.isEmpty() || result.last() < num) {
+                result.add(num)
+            } else {
+                result[binarySearch(result, num)] = num
+            }
+        }
+
+        return result.size
+    }
+
+    @Test
+    fun name() {
+        // lengthOfLIS(intArrayOf(10,9,2,5,3,7,101,18)) shouldBe 4
+        // lengthOfLIS(intArrayOf(0,1,0,3,2,3)) shouldBe 4
+        // lengthOfLIS(intArrayOf(0,1,2,3,4,5,6,7)) shouldBe 8
+        lengthOfLIS(intArrayOf(4,10,4,3,8,9)) shouldBe 3
+    }
+}