Exercise 1729Combinatorics › Inclusion-exclusionOlympiadAdded 3 Nov 2026
Two obstacles via IE
#IE#paths#obstacles
Statement
Count paths from to avoiding both and .
Hint
IE on the two points.
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Solution
Total. .
Through . .
Through . .
Through both. Paths through then ? is reachable from by moving right+up. .
Avoid. .
Conclusion. paths avoid both obstacles.