Done Hashing-2

contiguous.py

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+# Time Complexity : O(n)
+# Space Complexity : O(n)
+# Did this code successfully run on Leetcode : Yes
+# Any problem you faced while coding this : No
+# Approach: Convert 0 to -1 and 1 to +1 and compute prefix sum.
+# Store first occurrence of each prefix sum in hashmap to maximize length.
+
+class Solution:
+    def findMaxLength(self, nums: List[int]) -> int:
+        max_len = 0
+        h_map = {}
+        c_sum = 0
+
+        for i in range(len(nums)):
+            if nums[i] == 0:
+                c_sum -= 1
+            else:
+                c_sum += 1
+
+            if c_sum == 0:
+                max_len = i + 1
+            elif c_sum in h_map:
+                max_len = max(max_len, i - h_map[c_sum])
+            else:
+                h_map[c_sum] = i
+
+        return max_len

longestPalindrome.py

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+# Time Complexity : O(n)
+# Space Complexity : O(1)
+# Did this code successfully run on Leetcode : Yes
+# Any problem you faced while coding this : No
+# Approach: Count frequency of each character.
+# For even frequencies, use all occurrences.
+# For odd frequencies, use (count - 1) to keep it even.
+# If at least one odd frequency exists, we can place one character in the center.
+
+class Solution:
+    def longestPalindrome(self, s: str) -> int:
+        freq_cnt = [0] * 256
+
+        for i in s:
+            freq_cnt[ord(i)] += 1
+
+        max_cnt = 0
+        has_odd = False
+
+        for i in freq_cnt:
+            if i % 2 == 0:
+                max_cnt += i
+            else:
+                max_cnt += (i - 1)
+                has_odd = True
+
+        if has_odd:
+            max_cnt += 1
+
+        return max_cnt

subarrayEqualsK.py

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+# Time Complexity : O(n)
+# Space Complexity : O(n)
+# Did this code successfully run on Leetcode : Yes
+# Any problem you faced while coding this : No
+# Approach: Use prefix sum + hashmap. At each index, compute cumulative sum.
+# Store frequency of each prefix sum to handle multiple matches.
+
+class Solution:
+    def subarraySum(self, nums: List[int], k: int) -> int:
+        h_map = {0: 1}
+        c_sum = 0
+        res = 0
+
+        for i in nums:
+            c_sum += i
+            if (c_sum - k) in h_map:
+                res += h_map[c_sum - k]
+
+            if c_sum not in h_map:
+                h_map[c_sum] = 1
+            else:
+                h_map[c_sum] += 1
+
+        return res