Upload on 3/10

Author: gyb1325

13. Roman to Integer.py

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+class Solution:
+
+    def romanToInt(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        s = str(s)
+        lst1 = {'CM': 900, 'CD': 400, 'XL': 40, 'XC': 90, 'IV': 4, 'IX': 9}
+        lst2 = {'I': 1, 'V': 5, 'X': 10, 'L': 50, 'C': 100, 'D': 500, 'M': 1000}
+
+        if not s:
+            return 0
+        if len(s) == 1:
+            return lst2[s]
+        i = 0
+        sum = 0
+        while i <= len(s) - 1:
+            if len(s[i:]) >= 2 and s[i:i + 2] in lst1:
+                sum += lst1[s[i:i + 2]]
+                i += 2
+            else:
+                sum += lst2[s[i]]
+                i += 1
+        return sum

14. Longest Common Prefix.py

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+class Solution:
+
+    def longestCommonPrefix(self, strs: List[str]) -> str:
+        if not strs:
+            return ""
+        steps = len(strs[0])
+        t_flag = False
+        prefix = ""
+        for i in range(steps):
+            for j in range(1, len(strs)):
+                if len(strs[j]) > i:
+                    if strs[j][i] != strs[0][i]:
+                        t_flag = True
+                        break
+                else:
+                    t_flag = True
+                    break
+            if t_flag:
+                break
+            else:
+                prefix = prefix + strs[0][i]
+
+        return prefix

15. 3Sum.py

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+class Solution:
+
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        res = []
+        nums.sort()
+        N = len(nums)
+        for i in range(N):
+            if i > 0 and nums[i] == nums[i - 1]:
+                continue
+            target = -nums[i]
+            s = i + 1
+            e = N - 1
+            while s < e:
+                if nums[s] + nums[e] == target:
+                    res.append([nums[i], nums[s], nums[e]])
+                    s += 1
+                    while s < e and nums[s] == nums[s - 1]:
+                        s += 1
+                elif nums[s] + nums[e] < target:
+                    s += 1
+                else:
+                    e -= 1
+        return res

16. 3Sum Closest.py

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+class Solution:
+
+    def threeSumClosest(self, nums: List[int], target: int) -> int:
+        nums.sort()
+        N = len(nums)
+        closest = (float("inf"), 0)
+        for i in range(N):
+            new_target = target - nums[i]
+            s = i + 1
+            e = N - 1
+            while s < e:
+                diff = new_target - nums[s] - nums[e]
+                if diff == 0:
+                    return target
+                abs_diff = abs(diff)
+                if abs_diff < closest[0]:
+                    closest = (abs_diff, nums[i] + nums[s] + nums[e])
+                if diff > 0:
+                    s += 1
+                else:
+                    e -= 1
+        return closest[1]