Leetcode:n-queens II Problem Solving report

N-queens II (Level 4 difficulty levels, superlative 5)

Follow up for n-queens problem.

Now, instead outputting board configurations, return the totalnumber of distinct solutions.

Answer:
The solution to the first question is similar, and the difference is that the return value of the DFS is the number of solutions. Every time we search our 8 locations,
Add the 8-position solution together. There is no solution to the position, its return value is 0.

Also note base case:
When row = = size, that is, row is out of bounds, this means that the whole n-queen is full, we should return the solution to 1. because
You do not need any action, that is, the only solution is to remain intact. (although a bit difficult to understand), students can back to the previous layer to think
For example, the last line, you put a queen, it is a solution, so where DFS to the next layer should return 1.

1  Public classSolution {2      Public intTotalnqueens (intN) {3         if(n = = 0) {4             return0;5         }6         7         //Bug 1:forget To modify the parameters of the function.8         returnDFS (n, 0,NewArraylist<integer>());9     }Ten      One      Public intDfsintNintRow, arraylist<integer>path) { A         if(Row = =N) { -             //The base case: When the last line, the Queen has only 1 ways of putting (or not putting) -             return1; the         } -          -         intnum = 0; -          +         //The Queen can select any of the slot. -          for(inti = 0; I < n; i++) { +             if(!isValid (path, i)) { A                 Continue; at             } - Path.add (i); -              -             //All of the solutions is a possiablities is add up. -num + = DFS (n, row + 1, path); -Path.remove (Path.size ()-1); in         } -          to         returnnum; +     } -      the      Public BooleanIsValid (arraylist<integer> Path,intCol) { *         intSize =path.size (); $          for(inti = 0; i < size; i++) {Panax Notoginseng             //The same column with any of the current queen. -             if(col = =Path.get (i)) { the                 return false; +             } A              the             //diagonally lines. +             //Bug 2:forget to add a ') ' -             if(Size-i = = Math.Abs (Col-Path.get (i))) { $                 return false; $             } -         } -          the         return true; -     }Wuyi}

View Code

GITHUB:

Https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/dfs/totalNQueens_1218_2014.java

Leetcode:n-queens II Problem Solving report