[parkhojeong] WEEK 07 Solutions

longest-substring-without-repeating-characters/parkhojeong.py

@@ -0,0 +1,22 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        if s == "":
+            return 0
+
+        ch_to_idx = {}
+        start_idx = 0
+
+        i = 0
+        length_of_longest_substring = 1
+        for i in range(len(s)):
+            ch = s[i]
+            if ch in ch_to_idx and ch_to_idx[ch] >= start_idx:
+                start_idx = ch_to_idx[ch] + 1
+                ch_to_idx[ch] = i
+            else:
+                ch_to_idx[ch] = i
+                length_of_substring = i - start_idx + 1
+                length_of_longest_substring = max(length_of_longest_substring, length_of_substring)
+
+        return length_of_longest_substring
+

number-of-islands/parkhojeong.py

@@ -0,0 +1,26 @@
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        row_len = len(grid)
+        col_len = len(grid[0])
+
+        def dfs(row: int, col: int):
+            if not (0 <= row < row_len and 0 <= col < col_len):
+                return
+
+            if grid[row][col] == "0":
+                return
+
+            grid[row][col] = "0"
+            dfs(row - 1, col)
+            dfs(row + 1, col)
+            dfs(row, col - 1)
+            dfs(row, col + 1)
+
+        num_islands = 0
+        for row in range(row_len):
+            for col in range(col_len):
+                if grid[row][col] == "1":
+                    num_islands += 1
+                    dfs(row, col)
+
+        return num_islands

reverse-linked-list/parkhojeong.py

@@ -0,0 +1,16 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev_node, cur_node = None, head
+
+        while cur_node:
+            next_node = cur_node.next
+
+            cur_node.next = prev_node
+            prev_node, cur_node = cur_node, next_node
+
+        return prev_node

set-matrix-zeroes/parkhojeong.py

@@ -0,0 +1,34 @@
+class Solution:
+    def setZeroes(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+
+        row_len = len(matrix)
+        col_len = len(matrix[0])
+        MARKER = sys.maxsize
+
+        def dfs(row, col, d_row, d_col):
+            if not (0 <= row < row_len and 0 <= col < col_len):
+                return
+
+            if matrix[row][col] == 0:
+                return
+
+            matrix[row][col] = MARKER
+            dfs(row + d_row, col + d_col, d_row, d_col)
+
+        for row in range(row_len):
+            for col in range(col_len):
+                if matrix[row][col] == 0:
+
+                    matrix[row][col] = MARKER
+                    dfs(row + 1, col, 1, 0)
+                    dfs(row - 1, col, -1, 0)
+                    dfs(row, col + 1, 0, 1)
+                    dfs(row, col - 1, 0, -1)
+
+        for row in range(row_len):
+            for col in range(col_len):
+                if matrix[row][col] == MARKER:
+                    matrix[row][col] = 0

unique-paths/parkhojeong.py

@@ -0,0 +1,10 @@
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        column = [1] * m
+
+        for col in range(n - 1):
+
+            for row in range(1, m):
+                column[row] = column[row] + column[row - 1]
+
+        return column[-1]