001. Two Sum (go)

转职1年开发后，回头看原来写的代码，当初还是留下了一些小的瑕疵，优化空间很大……

原先：

func twoSumOrg(nums []int, target int) []int {
   numMap := make(map[int]int)
   result := make([]int, 2)

   for i, num := range nums {
      _, ok := numMap[num]
      if ok {
         result[0], result[1] = i, numMap[num]
      } else {
         numMap[target-num] = i
      }
   }

   return result
}

现在：

func twoSum(nums []int, target int) []int {
   numMap := make(map[int]int, len(nums))
   result := make([]int, 2)

   for i, num := range nums {
      _, ok := numMap[num]
      if ok {
         result[0], result[1] = i, numMap[num]
         break      } else {
         numMap[target-num] = i
      }
   }

   return result
}
对比结果：
Benchmark_twoSum-8       20000000         87.5 ns/op
Benchmark_twoSumOrg-8    10000000        137 ns/op

并且，还能进一步优化：

func twoSum(nums []int, target int) []int {
   numMap := make(map[int]int)
   result := make([]int, 2)

   for i, num := range nums {
      _, ok := numMap[num]
      if ok {
         result[0], result[1] = i, numMap[num]
         break      } else {
         numMap[target-num] = i
      }
   }

   return result
}

Benchmark_twoSum-8       20000000         84.0 ns/op