Leetcode 1449. Form Largest Integer With Digits That Add up to Target

Given costs for digits 1–9 and a total budget target, return the largest possible positive integer (as a string) whose digits' costs sum exactly to target, or "0" if impossible. This is an exact-knapsack dynamic programming problem: maximize the number (length) of digits and then pick the lexicographically/largest numeric arrangement (prefer higher digits) while ensuring feasibility for the remaining cost.