217 improve

利用映射保存记录，时间缩短到43ms

Author: aQua

Algorithms/0217.contains-duplicate/contains-duplicate.go

@@ -1,12 +1,12 @@
 package Problem0217
 
 func containsDuplicate(nums []int) bool {
+	m := make(map[int]bool, len(nums))
 	for i := 0; i < len(nums); i++ {
-		for j := i + 1; j < len(nums); j++ {
-			if nums[i] == nums[j] {
-				return true
-			}
+		if ok := m[nums[i]]; ok {
+			return true
 		}
+		m[nums[i]] = true
 	}
 
 	return false