Create 41. First Missing Positive (#440)

Author: Chayandas07

41. First Missing Positive

@@ -0,0 +1,20 @@
+class Solution {
+public:
+    int firstMissingPositive(std::vector<int>& nums) {
+        int n = nums.size();
+        unordered_map<int,bool> mp;
+        // Finding the maximum element in nums
+        int maxi = *max_element(nums.begin(), nums.end());
+        // Populating the unordered_map with values from nums
+        for(auto &num : nums){
+            mp[num] = true;
+        }
+        // Checking for the first missing positive integer
+        for(int i=1; i<maxi; i++){
+            if(mp.find(i) == mp.end())
+                return i;
+        }
+        // If all integers from 1 to maxi are present, return maxi+1
+        return maxi < 0 ? 1 : maxi+1;
+    }
+};