The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.
Given an integer n, return the number of distinct solutions to the n-queens puzzle.
Example:
Input: 4
Output: 2
Explanation: There are two distinct solutions to the 4-queens puzzle as shown below.
[
[".Q…", // Solution 1
“…Q”,
“Q…”,
“…Q.”],
["…Q.", // Solution 2
“Q…”,
“…Q”,
“.Q…”]
]
解题思路
- 回溯
func available(current []int, index int) bool {
n := len(current)
for i, v := range current {
// 同一列
if index == v {
return false
}
// 对角线
if (n-i) == index-v || (n-i) == v-index {
return false
}
}
return true
}
func core(current []int, n int, cnt *int) {
if len(current) == n {
*cnt += 1
}
for i := 0; i < n; i++ {
if available(current, i) {
core(append(current, i), n, cnt)
}
}
}
func totalNQueens(n int) int {
cnt := 0
if n == 0 {
return cnt
}
core([]int{}, n, &cnt)
return cnt
}