solution for problem first missing positive no cpp

algorithms/cpp/first_missing_positive.cpp

@@ -0,0 +1,37 @@
+// problem : https://leetcode.com/problems/first-missing-positive/
+
+class Solution {
+public:
+    int firstMissingPositive(vector<int>& nums) {
+        long int l = nums.size();
+        if(l==0)
+            return 1;
+        if(l==1)
+            return nums[0]==1?2:1;
+        long int f=0,i;
+        for( i=0;i<l;i++)
+        {
+            if(nums[i]<=0)
+            {
+                long int v= nums[i];
+                nums[i]=nums[f];
+                nums[f]=v;
+                f++;
+            }
+        }
+        long int st=f;
+        cout<<f<<" ";
+        for(int i=f;i<l;i++)
+        {
+            long int in = abs(nums[i])-1+st;
+            cout<<in<<" ";
+            if(in<l&&nums[in]>=0)
+                nums[in]=-nums[in];
+        }
+
+        for(int i=st;i<l;i++)
+            if(nums[i]>=0)
+                return i+1-st;
+        return l+1-st;
+    }
+};