[EGON] Week 02 Solutions

construct-binary-tree-from-preorder-and-inorder-traversal/EGON.py

@@ -0,0 +1,84 @@
+from typing import List, Optional
+from unittest import TestCase, main
+
+
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+        return self.solve_1(preorder, inorder)
+
+    """
+    Runtime: 112 ms (Beats 66.16%)
+    Time Complexity: O(n ** 2)
+    Space Complexity: O(n)
+    Memory: 52.83 MB (Beats 63.14%)
+    """
+    def solve_1(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+        index = 0
+
+        def build_tree(preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
+            nonlocal index
+
+            if not inorder:
+                return None
+
+            if not 0 <= index < len(preorder):
+                return None
+
+            root = TreeNode(preorder[index])
+            index += 1
+            split_index = inorder.index(root.val)
+            root.left = build_tree(preorder, inorder[:split_index])
+            root.right = build_tree(preorder, inorder[split_index + 1:])
+
+            return root
+
+        return build_tree(preorder, inorder)
+
+
+class _LeetCodeTestCases(TestCase):
+    def test_1(self):
+        preorder = [3, 9, 20, 15, 7]
+        inorder = [9, 3, 15, 20, 7]
+        output = TreeNode(
+            val=3,
+            left=TreeNode(
+                val=9
+            ),
+            right=TreeNode(
+                val=20,
+                left=TreeNode(val=15),
+                right=TreeNode(val=7)
+            )
+        )
+        self.assertEqual(Solution.buildTree(Solution(), preorder, inorder), output)
+
+    def test_2(self):
+        preorder = [-1]
+        inorder = [-1]
+        output = TreeNode(
+            val=-1
+        )
+        self.assertEqual(Solution.buildTree(Solution(), preorder, inorder), output)
+
+    def test_3(self):
+        preorder = [1, 2]
+        inorder = [1, 2]
+        output = TreeNode(
+            val=1,
+            right=TreeNode(
+                val=2
+            )
+        )
+        self.assertEqual(Solution.buildTree(Solution(), preorder, inorder), output)
+
+
+if __name__ == '__main__':
+    main()

counting-bits/EGON.py

@@ -0,0 +1,39 @@
+from typing import List
+from unittest import TestCase, main
+
+
+class Solution:
+    def countBits(self, n: int) -> List[int]:
+        return self.solve_1(n)
+
+    """
+    Runtime: 78 ms (Beats 31.22%)
+    Time Complexity: O(n * log n), 크기가 n인 배열의 원소들에 대해 시행마다 크기가 2로 나누어지는 비트연산을 수행하므로
+    Space Complexity: O(1), 변수 저장 없이 바로 결과 반환
+    Memory: 23.26 MB (Beats 39.52%)
+    """
+    def solve_1(self, n: int) -> List[int]:
+        def count_number_of_1(n: int):
+            count = 0
+            while n:
+                n &= (n - 1)
+                count += 1
+            return count
+
+        return [count_number_of_1(num) for num in range(n + 1)]
+
+
+class _LeetCodeTestCases(TestCase):
+    def test_1(self):
+        n = 2
+        output = [0, 1, 1]
+        self.assertEqual(Solution.countBits(Solution(), n), output)
+
+    def test_2(self):
+        n = 5
+        output = [0, 1, 1, 2, 1, 2]
+        self.assertEqual(Solution.countBits(Solution(), n), output)
+
+
+if __name__ == '__main__':
+    main()

counting-bits/EGON.swift

@@ -0,0 +1,113 @@
+import Foundation
+
+class Solution {
+    func countBits(_ n: Int) -> [Int] {
+        return solve_2(n)
+    }
+
+    /*
+        **내장함수를 사용한 풀이**
+
+        Runtime: 37 ms (Beats 49.12%)
+        Time Complexity: O(n * log n)
+            - 길이가 n인 range를 순회하므로 O(n)
+            - 정수에 대해 non zero bit를 세는데 O(log n)
+            > O(n * log n)
+        Space Complexity: O(n)
+            - 배열에 값을 저장하며 크기가 n이 되므로 O(n)
+        Memory: 20.86 MB (Beats 90.106%)
+    */
+    func solve_1(_ n: Int) -> [Int] {
+        var result: [Int] = []
+        for num in 0...n {
+            result.append(num.nonzeroBitCount)
+        }
+        return result
+    }
+
+    /*
+        ** Brian Kernighan's Algorithm을 사용한 풀이 **
+
+        Runtime: 39 ms (Beats 42.11%)
+        Time Complexity: O(n * log n)
+            - 길이가 n인 range를 순회하므로 O(n)
+            - bitCountWithBrianKernighan 에서 내부 while문 실행마다 num이 절반으로 줄어드므로, 실행횟수는 O(log n)
+            > O(n * log n)
+        Space Complexity: O(n)
+            - 배열에 값을 저장하며 크기가 n이 되므로 O(n)
+        Memory: 16.01 MB (Beats 67.84%)
+    */
+    func solve_2(_ n: Int) -> [Int] {
+
+        func bitCountWithBrianKernighan(_ num: Int) -> Int {
+            var num = num
+            var bitCount = 0
+            while 0 < num {
+                num &= (num - 1)
+                bitCount += 1
+            }
+
+            return bitCount
+        }
+
+        var result: [Int] = []
+        for num in 0...n {
+            result.append(bitCountWithBrianKernighan(num))
+        }
+        return result
+    }
+
+    /*
+        ** MSB에 대해 DP를 사용한 풀이 **
+        > num의 비트 카운트 = MSB의 비트 카운트(1 고정) + (num - msb)의 비트 카운트
+
+        Runtime: 36 ms (Beats 58.48%)
+        Time Complexity: O(n)
+            - 0부터 n까지 range를 순회하므로 O(n)
+            > O(n)
+        Space Complexity: O(n)
+            - 길이가 n인 dp 배열을 저장하므로 O(n)
+        Memory: 21.15 MB (Beats 67.84%)
+    */
+    func solve_3(_ n: Int) -> [Int] {
+        guard 1 <= n else { return [0] }
+
+        var dp = [Int](repeating: 0, count: n + 1)
+        var msb = 1
+        for num in 1...n {
+            if msb << 1 == num {
+                msb = num
+            }
+
+            dp[num] = 1 + dp[num - msb]
+        }
+
+        return dp
+    }
+
+    /*
+        ** LSB에 대해 DP를 사용한 풀이 **
+        > num의 비트 카운트 = num을 right shift한 숫자의 비트 카운트 + LSB의 비트 카운트(1 또는 0)
+
+        Runtime: 28 ms (Beats 97.08%)
+        Time Complexity: O(n)
+            - 0부터 n까지 range를 순회하므로 O(n)
+            > O(n)
+        Space Complexity: O(n)
+            - 길이가 n인 dp 배열을 저장하므로 O(n)
+        Memory: 21.26 MB (Beats 53.80%)
+    */
+    func solve_4(_ n: Int) -> [Int] {
+        guard 1 <= n else { return [0] }
+
+        var dp = [Int](repeating: 0, count: n + 1)
+        for num in 1...n {
+            dp[num] = dp[num >> 1] + (num & 1)
+        }
+
+        return dp
+    }
+}
+
+let solution = Solution()
+print(solution.solve_4(0))

decode-ways/EGON.py

@@ -0,0 +1,65 @@
+from typing import List
+from unittest import TestCase, main
+
+
+class Solution:
+    def numDecodings(self, s: str) -> int:
+        return self.solve_1(s)
+
+    """
+    Runtime: 32 ms (Beats 80.36%)
+    Time Complexity: O(n)
+    Space Complexity: O(n)
+    Memory: 16.59 MB (Beats 51.72%)
+    """
+    def solve_1(self, s: str) -> int:
+        if len(s) == 0:
+            return 0
+
+        if len(s) == 1:
+            return 0 if int(s) == 0 else 1
+
+        if len(s) == 2:
+            last_one_digit, last_two_digits = int(s[1]), int(s)
+            if last_one_digit == 0:
+                return 1 if 10 <= last_two_digits <= 26 else 0
+            else:
+                if 0 <= last_two_digits < 10:
+                    return 0
+                elif 10 <= last_two_digits <= 26:
+                    return 2
+                else:
+                    return 1
+
+        dp = [0] * (len(s) + 1)
+        dp[0], dp[1], dp[2] = self.solve_1(s[:0]), self.solve_1(s[:1]), self.solve_1(s[:2])
+        for i in range(3, len(s) + 1):
+            last_one_digit, last_two_digits = int(s[i - 1]), int(s[i - 2: i])
+            last_two_digits = int(s[i - 2: i])
+            if last_one_digit == 0:
+                dp[i] += dp[i - 2] if 10 <= last_two_digits <= 26 else 0
+            else:
+                dp[i] += dp[i - 1] + (dp[i - 2] if 10 <= last_two_digits <= 26 else 0)
+
+        return dp[-1]
+
+
+class _LeetCodeTestCases(TestCase):
+    def test_1(self):
+        s = "226"
+        output = 3
+        self.assertEqual(Solution.numDecodings(Solution(), s), output)
+
+    def test_2(self):
+        s = "2101"
+        output = 1
+        self.assertEqual(Solution.numDecodings(Solution(), s), output)
+
+    def test_3(self):
+        s = "06"
+        output = 0
+        self.assertEqual(Solution.numDecodings(Solution(), s), output)
+
+
+if __name__ == '__main__':
+    main()