算法证明——从n位数字中删除k位数字后生成最小数字

Problem: given an n-digit number, which k (k < n) digits should be deleted from it to make the number left is the smallest among all cases (the relative sequence of remaining digits should not be changed). e.g. delete 2 digits from '24635', the smallest left number is '235'.Problem: given an n-digit number, which k (