数学归纳法
递归
回溯
class Solution {
func judgePoint24(_ nums: [Int]) -> Bool {
let result = nums.map { (item) -> Double in
return Double(item)
}
return solve(nums: result)
}
func solve(nums: [Double]) -> Bool {
guard nums.count != 0 else {
return false
}
guard nums.count != 1 else {
return abs(nums[0]) - 24.0 < 0.000001;
}
for (offset, element) in nums.enumerated() {
for (offset2, element2) in nums.enumerated() {
guard offset != offset2 else { continue }
var nums2 = [Double]()
for (offset3, element3) in nums.enumerated() where offset3 != offset && offset3 != offset2 {
nums2.append(element3)
}
for i in 0...3 {
if i<2 && offset2 > offset {
continue
}
switch i {
case 0:
nums2.append(element + element2)
case 1:
nums2.append(element * element2)
case 2:
nums2.append(element - element2)
case 3:
guard element2 != 0 else { continue }
nums2.append(element / element2)
default:
break
}
if solve(nums: nums2) {
print(nums2)
return true
}
nums2.removeLast()
}
}
}
return false
}
}
var nums = [8, 1, 6, 6]
let solution = Solution.init()
let result = solution.judgePoint24(nums)
print(result)
