boj Segment Tree bid shading greedy DP 이직 surplus maximization univariate Recommender System negative sampling pytorch gradient descent time series Backpropagation BF 자료구조 winning price estimation ML 경진대회 ndcg implicit recommendation cross entropy loss dbscan tbats state space model univariate time series Fluentbit 우아콘 Exponential smoothing Dacon Maximum Likelihood Estimation Matrix Factorization cross entropy cost function scikit-learn docker deep learning 부분합 softmax Information Theory derivative Convolution ETS container regression implicit gradient Logging Code Analysis ml Pipeline vm 시뮬레이션 ctr image 구현 map