Merge pull request #373 from YeonguChoe/main

2주차 풀이

Author: YeonguChoe

construct-binary-tree-from-preorder-and-inorder-traversal/yeonguchoe.go

@@ -0,0 +1,36 @@
+func indexOf(slice []int, value int) int {
+    for i, v := range slice {
+        if v == value {
+            return i
+        }
+    }
+    return -1
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+    if len(preorder) == 0 || len(inorder) == 0 {
+        return nil
+    }
+
+    // Preorder의 처음 값으로 root을 만듬
+    rootVal := preorder[0]
+    root := &TreeNode{Val: rootVal}
+
+    // inorder에서 root의 위치를 찾음
+    mid := indexOf(inorder, rootVal)
+
+    // inorder에서 mid의 왼쪽은 left subtree이고 오른쪽은 right subtree이다.
+    leftInorder := inorder[:mid]
+    rightInorder := inorder[mid+1:]
+
+    // left preorder를 계산한다.
+    leftPreorder := preorder[1 : len(leftInorder)+1]
+    // right preorder를 계산한다.
+    rightPreorder := preorder[len(leftInorder)+1:]
+
+    // tree 만들기
+    root.Left = buildTree(leftPreorder, leftInorder)
+    root.Right = buildTree(rightPreorder, rightInorder)
+
+    return root
+}

counting-bits/yeonguchoe.go

@@ -0,0 +1,11 @@
+func countBits(n int) []int {
+	var result []int = make([]int, n+1)
+	var offset int = 1
+	for i := 1; i <= n; i++ {
+		if i == offset*2 {
+			offset = offset * 2
+		}
+		result[i] = 1 + result[i-offset]
+	}
+	return result
+}

decode-ways/yeonguchoe.go

@@ -0,0 +1,32 @@
+func dfs(s string, i int, memo map[int]int) int {
+	if i == len(s) {
+		return 1
+	}
+	if val, found := memo[i]; found {
+		return val
+	}
+	if s[i] == '0' {
+		memo[i] = 0
+		return 0
+	}
+
+	// 1자리 숫자로 디코딩
+	result := dfs(s, i+1, memo)
+
+	// 2자리 숫자로 디코딩
+	if i+1 < len(s) {
+		// 10의 자리 숫자 또는 20의 자리 숫자로 디코딩
+		if (s[i] == '1') || (s[i] == '2' && s[i+1] >= '1' && s[i+1] <= '6') {
+			result += dfs(s, i+2, memo)
+		}
+	}
+	// dp에 저장
+	memo[i] = result
+	return result
+}
+
+func numDecodings(s string) int {
+	// memo 테이블 만들고 dfs 호출
+	memo := make(map[int]int)
+	return dfs(s, 0, memo)
+}

encode-and-decode-strings/yeonguchoe.go

@@ -0,0 +1,33 @@
+type Codec struct {
+}
+
+// Encodes a list of strings to a single string.
+func (codec *Codec) Encode(strs []string) string {
+	var temp []rune
+	for _, v := range strs {
+		var current_string = []rune(v)
+		temp = append(temp, rune(len(current_string)))
+		temp = append(temp, rune('π'))
+		temp = append(temp, current_string...)
+	}
+	return string(temp)
+}
+
+// Decodes a single string to a list of strings.
+func (codec *Codec) Decode(strs string) []string {
+	var full_string = []rune(strs)
+	var result []string
+
+	var index = 0
+
+	for index < len(full_string) {
+		var word_start int = int(index)
+		for full_string[word_start] != rune('π') {
+			word_start += 1
+		}
+		length := int(full_string[word_start-1])
+		result = append(result, string(full_string[word_start+1:word_start+1+length]))
+		index = word_start + 1 + length
+	}
+	return result
+}

valid-anagram/yeonguchoe.go

@@ -0,0 +1,27 @@
+func isAnagram(s string, t string) bool {
+
+	var s_frequency map[rune]int = make(map[rune]int)
+	var t_frequency map[rune]int = make(map[rune]int)
+
+	for i := 0; i < len(s); i++ {
+		s_frequency[rune(s[i])] += 1
+	}
+
+	for index, key := range t {
+		t_frequency[key] += 1
+	}
+
+	for key, value := range s_frequency {
+		if v, key_exist := t_frequency[key]; !key_exist || v != value {
+			return false
+		}
+	}
+
+	for key, value := range t_frequency {
+		if v, key_exist := s_frequency[key]; !key_exist || v != value {
+			return false
+		}
+	}
+
+	return true
+}