Partition nums into two contiguous subarrays left and right such that every element in left <= every element in right. Return the length of left — the smallest such partition.
Input: Integer array nums.
Output: Length of smallest valid left partition.
Input: [5,0,3,8,6]
Output: 3
Explanation: left=[5,0,3], right=[8,6]. max(left)=5<=min(right)=6.Input: [1,1,1,0,6,12]
Output: 4
Explanation: left=[1,1,1,0], right=[6,12].Input: [1,2,3,4,5]
Output: 1
Explanation: left=[1], right=[2,3,4,5].2<=nums.length<=10^50<=nums[i]<=10^6