Solve leetcode 1, 217, 409, and 88

Author: codethecoffee

1-Two Sum.py

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+# Link: https://leetcode.com/problems/two-sum/
+
+def twoSum(nums, target):
+    # key: Number that adds up to target
+    # value: Index the number is at
+    two_sum = {}
+    
+    # Iterate through nums using indices b/c we need the indices
+    # for the final ans
+    for i in range(len(nums)):
+        curr_num = nums[i]
+        # Case 1: We found a pair that adds up to target
+        if curr_num in two_sum:
+            return [two_sum[curr_num], i]
+        # Case 2: Add a new entry for the current number
+        else:
+            two_sum[target-curr_num] = i
+    
+    # If we go through the entire for loop without returning
+    # there's no valid answer
+    return -1

217-Contains Duplicate.py

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+# Link: https://leetcode.com/problems/contains-duplicate/
+
+def containsDuplicate(nums):
+    # A set keeping track of the numbers encountered so far
+    num_seen = set()
+    
+    for curr_num in nums:
+        # Case 1: We have seen curr_num earlier on in nums
+        if curr_num in num_seen:
+            return True
+        # Case 2: First encounter with curr_num
+        else:
+            num_seen.add(curr_num)
+    
+    # If we go through the entire for loop without returning
+    # there are no duplicates
+    return False

409-Longest Palindrome.py

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+# Link: https://leetcode.com/problems/longest-palindrome/
+
+def longestPalindrome(s):
+    # key: unique character
+    # value: number of times said character occurs in s
+    char_count = {}
+    
+    # Populate the char_count dictionary
+    for char in s:
+        if char in char_count:
+            char_count[char] += 1
+        else:
+            char_count[char] = 1
+    
+    palindrome = 0 # Length of the longest palindrome
+    odd = False # Whether there's at least one odd num occ char
+    
+    for count in char_count.values():
+        # Case 1: The current character occurs an odd number of times
+        if count%2 != 0:
+            odd = True # Set odd flag
+            # Add an even number of those characters
+            palindrome += (count-1)
+        # Case 2: The current character occurs an even number of times
+        else:
+            palindrome += count
+    
+    # If we encountered at least one oddly occuring character
+    if odd:
+        # Add 1 since you can have an odd number of chars in the middle
+        # of the palindrome
+        palindrome += 1
+    
+    return palindrome

88-Merge Sorted Array.py

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+# https://leetcode.com/problems/merge-sorted-array/
+
+def merge(nums1, m, nums2, n):
+    # Iterate through both of the sorted arrays at the same time
+    while m > 0 and n > 0:
+        curr_1 = nums1[m-1]
+        curr_2 = nums2[n-1]
+
+        if curr_1 >= curr_2:
+            nums1[(m+n)-1] = curr_1
+            m -= 1
+        else: # curr_2 > curr_1
+            nums1[(m+n)-1] = curr_2
+            n -= 1
+    
+    # If there are smaller elements left in nums2, copy them over.
+    # No need to do this for leftover num1 elements, since we're
+    # merging into nums1 and the elements will already be there.
+    while n > 0:
+        nums1[n-1] = nums2[n-1]
+        n -= 1
+    
+    return nums1