Codeforces 1082F - Speed Dial - 动态规划
Polycarp's phone book contains $n$ phone numbers, each of them is described by $s_i$ — the number itself and $m_i$ — the number of times Polycarp dials it in daily.
Polycarp has just bought a brand new phone with an amazing speed dial feature! More precisely, $k$ buttons on it can have a number assigned to it (not necessary from the phone book). To enter some number Polycarp can press one of these $k$ buttons and then finish the number using usual digit buttons (entering a number with only digit buttons is also possible).
Speed dial button can only be used when no digits are entered. No button can have its number reassigned.
What is the minimal total number of digit number presses Polycarp can achieve after he assigns numbers to speed dial buttons and enters each of the numbers from his phone book the given number of times in an optimal way?