CSES - Walkthrough

Make array non-decreasing by only increasing elements. find the lowest sum of increases. Simpler than Sonya: we can only increase, not decrease. The DP is asymmetric. $dp[i][x]$ = min cost for first $i$ elements, last value $\leq x$.

But we only pay for increases: cost = $\max(0, x - a_i)$. Slope trick: track where the optimal $x$ lies. It's always at a breakpoint (one of the $a_i$ values). Use heap to maintain.