CPP version of MEX value of array in O(1) space

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Author: rachitiitr

LeetCode/41.first-missing-positive.cpp

@@ -0,0 +1,18 @@
+// Check Youtube video for video explanation
+class Solution {
+public:
+    int firstMissingPositive(vector<int> A)
+    {
+        int n = A.size();
+        for(int i = 0; i < n; ++ i) {
+            while(A[i] >= 1 && A[i] <= n && A[i] != i+1)
+                swap(A[i], A[A[i] - 1]);
+        }
+        
+        for(int i = 0; i < n; ++ i)
+            if(A[i] != i + 1)
+                return i + 1;
+        
+        return n + 1;
+    }
+};