Create 268_Missing_Number.cc

https://leetcode.com/problems/missing-number/

Author: cpppy

268_Missing_Number.cc

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+class Solution {
+public:
+    int missingNumber(vector<int>& nums) {
+        sort(nums.begin(),nums.end());
+        if(nums[0]!=0)   return 0;
+        for(int i=0;i<nums.size()-1;++i){
+            if(nums[i]!=nums[i+1]-1){
+                return nums[i]+1;
+            }
+        }
+        return nums[nums.size()-1]+1;
+    }
+};