747. Largest Number At Least Twice of Others

 static int wing=[]()
 {
     std::ios::sync_with_stdio(false);
     cin.tie(NULL);
     return ;
 }();

 class Solution
 {
 public:
     int dominantIndex(vector<int>& nums)
     {
         int firstmax=INT_MIN,secondmax=INT_MIN,index=-;
         int sz=nums.size();
         for(int i=;i<sz;i++)
         {
             if(nums[i]>firstmax)
             {
                 secondmax=firstmax;
                 firstmax=nums[i];
                 index=i;
             }
             else if(nums[i]>secondmax)
                 secondmax=nums[i];
         }
         return (firstmax>=*secondmax)? index:-;
     }
 };

扫描一遍，找出最大和第二大的就行了