Assign values from specified domains to variables so that all stated constraints hold simultaneously. A partial assignment can be rejected when it violates a constraint or leaves an unassigned variable with no permissible value. Backtracking applies this test during a depth-first search.
A finite constraint satisfaction problem on a array. Each entry must be one of the integers , and every row, column, and designated box must contain each value once. Given entries constrain the possible completions; backtracking searches those completions.
Choose an unassigned variable with the fewest currently legal values. No legal values detects failure immediately; exactly one legal value forces a choice. This ordering can reduce the search tree without changing the set of solutions.
