Online algorithm for calculating standard deviation
问题 Normally, I have a more technical problem but I will simplify it for you with an example of counting balls. Assume I have balls of different colors and one index of an array (initialized to all 0's) reserved for each color. Every time I pick a ball, I increment the corresponding index by 1. Balls are picked randomly and I can only pick one ball at a time. My sole purpose is to count number of balls for every color, until I run out of balls. I would like to calculate standard deviation of the