03: Longest Substring Without Repeating Characters

Go/leetcode.go

@@ -234,10 +234,7 @@ func IsValidParentheses(s string) bool {
 		}
 	}
 
-	if len(stack) > 0 {
-		return false
-	}
-	return true
+	return len(stack) == 0
 }
 
 // 217. Contains Duplicate
@@ -254,3 +251,23 @@ func ContainsDuplicate(nums []int) bool {
 	}
 	return false
 }
+
+// 3. Longest Substring Without Repeating Characters
+// https://leetcode.com/problems/longest-substring-without-repeating-characters/?envType=problem-list-v2&envId=hash-table
+func LengthOfLongestSubstring(s string) int {
+	charIndex := make(map[rune]int)
+	maxLen := 0
+	start := 0
+	for idx, ch := range []rune(s) {
+		if lastIndex, found := charIndex[ch]; found && lastIndex >= start {
+			start = lastIndex + 1
+		}
+		charIndex[ch] = idx
+
+		if idx-start+1 > maxLen {
+			maxLen = idx - start +1
+		}
+	}
+
+	return maxLen
+}

Go/leetcode_test.go

@@ -193,3 +193,30 @@ func Test_ContainsDuplicate(t *testing.T) {
 		}
 	}
 }
+
+// 3. Longest Substring Without Repeating Characters
+// https://leetcode.com/problems/longest-substring-without-repeating-characters/?envType=problem-list-v2&envId=hash-table
+func Test_LengthOfLongestSubstring(t *testing.T) {
+	tests := []struct {
+		s        string
+		expected int
+	}{
+		{"abcabcbb", 3},
+		{"bbbbb", 1},
+		{"pwwkew", 3},
+		{"", 0},
+		{"a", 1},
+		{"ab", 2},
+		{"dvdf", 3},
+		{"tmmzuxt", 5},
+		{" ", 1},
+	}
+
+	for _, test := range tests {
+		got := LengthOfLongestSubstring(test.s)
+		if got != test.expected {
+			t.Errorf("for %s got %d but want %d", test.s, got, test.expected)
+		}
+	}
+
+}

LeetCode/medium/longest_substring_without_repeat.py

@@ -0,0 +1,16 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        seen_map = {}
+        max_len = 0
+        win_start = 0
+
+        for idx, value in enumerate(s):
+            last_index = seen_map.get(value)
+            if last_index is not None and last_index >= win_start:
+                win_start = last_index + 1
+
+            seen_map[value] = idx
+
+            max_len = max(max_len, idx - win_start + 1)
+
+        return max_len

tests/test_leetcode_medium.py

@@ -0,0 +1,48 @@
+# test file for LeetCode medium problems
+
+import pytest
+
+# 03: Longest Substring Without Repeating Characters
+# https://leetcode.com/problems/longest-substring-without-repeating-characters/?envType=problem-list-v2&envId=hash-table
+
+
+@pytest.mark.parametrize(
+    "s, expected",
+    [
+        ("abcabcbb", 3),  # longest substring is "abc" with length 3
+        ("bbbbb", 1),  # longest substring is "b" with length 1
+        ("pwwkew", 3),  # longest substring is "wke" with length 3
+        ("", 0),  # empty string, longest substring is 0
+        ("abcdef", 6),  # entire string is the longest substring, length 6
+        ("aab", 2),  # longest substring is "ab", length 2
+        ("dvdf", 3),  # longest substring is "vdf", length 3
+        (" ", 1),  # single space character, length 1
+    ],
+)
+def test_length_of_longest_substring(s: str, expected: int):
+    from ..LeetCode.medium.longest_substring_without_repeat import Solution
+
+    solution = Solution()
+    assert solution.lengthOfLongestSubstring(s) == expected
+
+
+# 05: Longest Palindromic Substring
+# https://leetcode.com/problems/longest-palindromic-substring/?envType=problem-list-v2&envId=hash-table
+
+# 07: Reverse Integer
+# https://leetcode.com/problems/reverse-integer/?envType=problem-list-v2&envId=hash-table
+
+# 08: String to Integer (atoi)
+# https://leetcode.com/problems/string-to-integer-atoi/?envType=problem-list-v2&envId=hash-table
+
+# 09: Palindrome Number
+# https://leetcode.com/problems/palindrome-number/?envType=problem-list-v2&envId=hash-table
+
+# 10: Regular Expression Matching
+# https://leetcode.com/problems/regular-expression-matching/?envType=problem-list-v2&envId=hash-table
+
+# 11: Container With Most Water
+# https://leetcode.com/problems/container-with-most-water/?envType=problem-list-v2&envId=hash-table
+
+# 12: Integer to Roman
+# https://leetcode.com/problems/integer-to-roman/?envType=problem-list-v2&envId=hash-table

weekly_roundtable/array_hasing/nov_09_2025.py

@@ -0,0 +1,40 @@
+from typing import List
+
+
+class Solution:
+    def hasDuplicate(self, nums: List[int]) -> bool:
+        seen = {}  # {key: valu}
+
+        for val in nums:
+            gg = seen.get(val)
+            if gg:
+                return True
+            seen[val] = 1
+
+        return False
+
+    def isAnagram(self, s: str, t: str) -> bool:
+        if len(s) != len(t):
+            return False
+
+        s_map = {}
+        t_map = {}
+
+        for idx in range(len(s)):
+            s_char = s[idx]
+            t_chat = t[idx]
+
+            s_map[s_char] = s_map.get(s_char, 0) + 1
+            t_map[t_chat] = t_map.get(t_chat, 0) + 1
+
+        return s_map == t_map
+
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        hash_map = {}
+        for idx in range(len(nums)):
+            hash_map[nums[idx]] = idx
+
+        for idx in range(len(nums)):
+            diff = target - nums[idx]
+            if diff in hash_map and hash_map[diff] != idx:
+                return [idx, hash_map[diff]]