Place numbers from 1-N in all the cells in the grid so that the numbers do not repeat in any row and column. Then draw a closed loop that travels horizontally and vertically between the centers of adjacent cells and visits every cell exactly once. The numbers along the loop must follow the worm rule of alternating higher and lower values. The numbers on the left show the sums of the numbers on the loop segments in the given row (in the correct order).
(Rules and example (N=4) from WPC 2018 IB)
- With Obstacles: Some cells may remain empty. The number of "obstacles" is given.
History of the puzzle
Appeared on WPC 2018/Round 12, an "innovatives" round. The puzzle was written by František Luskač (Czech Rep.).
Appearances in the past WPCs
- WPC 2018/Round 12 (both with and without obstacles) by František Luskač