[Swift-2019力扣杯春季决赛]4. 有效子数组的数目

 1 class Solution {
 2     var ne:[Int] = [Int](repeating:0,count:50005)
 3     var st:[Int] = [Int](repeating:0,count:50005)
 4     var t:Int = 0
 5     func validSubarrays(_ nums: [Int]) -> Int {
 6         var n:Int = nums.count
 7         var ans:Int = 0
 8         st[0] = n
 9         for i in stride(from:(n - 1),through:0,by:-1)
10         {
11             while((t != 0) && nums[st[t]] >= nums[i])
12             {
13                 t -= 1
14             }
15             ne[i] = st[t]
16             t += 1
17             st[t] = i
18             ans += ne[i] - i
19         }
20         return ans
21     }
22 }