nqueues_ii
nqueues_ii.go 源码
package main
//N皇后问题II
//常规解法
func totalNQueens(n int) int {
shu, pie, na := make(map[int]bool), make(map[int]bool), make(map[int]bool)
var dfs func(n, i int, shu, pie, na map[int]bool)
res := 0
dfs = func(n, i int, shu, pie, na map[int]bool) {
if i == n {
res++
return
}
for j := 0; j < n; j++ {
if !shu[j] && !pie[i-j] && !na[i+j] {
shu[j], pie[i-j], na[i+j] = true, true, true
dfs(n, i+1, shu, pie, na)
shu[j], pie[i-j], na[i+j] = false, false, false
}
}
}
dfs(n, 0, shu, pie, na)
return res
}
//位运算
func totalNQueens2(n int) (ans int) {
var solve func(row, columns, diagonals1, diagonals2 int)
solve = func(row, columns, diagonals1, diagonals2 int) {
if row == n {
ans++
return
}
availablePositions := (1<<n - 1) &^ (columns | diagonals1 | diagonals2)
for availablePositions > 0 {
position := availablePositions & -availablePositions
solve(row+1, columns|position, (diagonals1|position)<<1, (diagonals2|position)>>1)
availablePositions &^= position
}
}
solve(0, 0, 0, 0)
return
}
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