数组a[n]中a[0:k]a[k+1:n]倒置 空间o(1)最坏时间复杂度o(n)

数列：x[] = [a][b][c][d][e][f][g]...[?] (长度n)     临时变量[]
1. set i = 0, j = n - 1
2. x[i] ==> []
3. x[j] ==> x[i]
4. [] ==> x[j]
5. i++, j--
6. i < j goto 1
7. end

貌似你不能确定后面就是K个数。