[Swift Weekly Contest 116]LeetCode962. 最大宽度坡 | Maximum Width Ramp

Given an array A of integers,a ramp is a tuple (i,j) for which i < j and A[i] <= A[j].  The width of such a ramp is j - i.

Find the maximum width of a ramp in A.  If one doesn‘t exist,return 0.

Example 1:

Input: [6,8,2,1,5]
Output: 4 Explanation: The maximum width ramp is achieved at (i,j) = (1,5): A[1] = 0 and A[5] = 5. 

Example 2:

Input: [9,9,4,1]
Output: 7 Explanation: The maximum width ramp is achieved at (i,j) = (2,9): A[2] = 1 and A[9] = 1.

Note:

1. 2 <= A.length <= 50000
2. 0 <= A[i] <= 50000

给定一个整数数组 A，坡是元组 (i,j)，其中  i < j 且 A[i] <= A[j]。这样的坡的宽度为 j - i。

找出 A 中的坡的最大宽度，如果不存在，返回 0 。

示例 1：

输入：[6,5]
输出：4
解释：
最大宽度的坡为 (i,5): A[1] = 0 且 A[5] = 5.

示例 2：

输入：[9,1]
输出：7
解释：
最大宽度的坡为 (i,9): A[2] = 1 且 A[9] = 1.

提示：

1. 2 <= A.length <= 50000
2. 0 <= A[i] <= 50000

440ms 

 1 class Solution {
 2     func maxWidthRamp(_ A: [Int]) -> Int {
 3         var val:[Int] = [Int]()
 4         var index:[Int] = [Int]()
 5         var n:Int = A.count
 6         var ans:Int = 0
 7         for i in 0..<n
 8         {
 9             var x:Int = A[i]
10             var left:Int = 0
11             var right:Int = val.count - 1
12             while(left < right)
13             {
14                 var mid:Int = (left + right) / 2
15                 if val[mid] <= x
16                 {
17                     right = mid
18                 }
19                 else
20                 {
21                     left = mid + 1
22                 }
23             }
24             if left <= right && val[left] <= x
25             {
26                 ans = max(ans,i - index[left])
27             }
28             if val.isEmpty || val.last! > x
29             {
30                 val.append(x)
31                 index.append(i)
32             }
33         }
34         return ans
35     }
36 }