Goal: place sources so every clue number equals the total signal in that cell. Each source has a peak at its own cell, then the signal decreases by 1 per step as it travels in the four cardinal directions (up, right, down, left). Signal travels in straight lines and is absorbed by walls. Signals from multiple sources add together. The small numbers in each cell show the current total signal from all sources. Only the clue cells matter for winning — match every clue exactly. Use exactly K sources. ✕