说明：  给定一个长度为n的整数数组a，元素均不相同，问数组是否存在这样一个片段，只将该片段翻转就可以使整个数组升序排列。其中数组片段[l,r]表示序列a[l], a[l+1],?...,?a[r]。原始数组为 a[1], a[2], ..., a[l-2], a[l-1], a[l], a[l+1], ..., a[r-1], a[r], a[r+1], a[r+2], ..., a[n-1], a[n]， 将片段[l,r]反序后的数组是 a[1], a[2], ..., a[l-2], a[l-1], a[r], a[r-1], ..., a[l+1], a[l], a[r+1], a[r+2], ..., a[n-1], a[n]。
(Given an integer array a with a length of N, the elements are all different, and ask if the array has such a fragment that turns the fragment to the entire array in ascending order. The array fragment [l and r] represent sequences a[l], a[l+1],..., and a[r]. The original array is A[1], a[2],..., a[l-2], a[l-1], a[l], a[l+1],..., a[r-1], a[r], a[r+1], a[r+2],..., a[n-1], a[n-1], The array of fragment [l, r] back sequence is A[1], a[2],..., a[l-2], a[l-1], a[r], a[r-1],..., a[l+1], a[l], a[r+1], a[r+2],..., a[n-1], a[n-1].)