Create: 41-First-Missing-Positive.py

python/41-First-Missing-Positive.py

@@ -0,0 +1,27 @@
+class Solution:
+    def firstMissingPositive(self, nums: List[int]) -> int:
+        A = nums
+        for i in range(len(A)):
+            if A[i] < 0:
+                A[i] = 0
+
+        for i in range(len(A)):
+            val = abs(A[i])
+            if 1 <= val <= len(A):
+                if A[val - 1] > 0:
+                    A[val - 1] *= -1
+                elif A[val - 1] == 0:
+                    A[val - 1] = -1 * (len(A) + 1)
+
+        for i in range( 1, len(A)+ 1):
+            if A[i -1] >= 0:
+                return i
+
+        return len(A) + 1
+
+    def firstMissingPositive_2(self, nums: List[int]) -> int:
+        new = set(nums)
+        i = 1
+        while i in new:
+            i += 1
+        return i