491 递增子序列
func findSubsequences(nums []int) [][]int {// 思路，在原数组上面找寻递增子序列，所以不能改变顺序，var path []intvar res [][]int//nums = quicksort(nums)backtracking(nums, &path, &res, -200) // 范围是【-100， 100】,传入一个不在区间的数字就不会重复return res
}func backtracking(nums []int, path *[]int, res *[][]int, last int) {if len(nums) == 0 {return}used := make(map[int]bool)for i:=0; i<len(nums); i++ {if used[nums[i]] {continue}if nums[i] < last{continue}*path = append(*path, nums[i])used[nums[i]] = trueif len(*path) > 1 {var copypath = make([]int, len(*path))copy(copypath, *path)*res = append(*res, copypath)}backtracking(nums[i+1 : ], path, res, nums[i])*path = (*path)[0 : len(*path) - 1]}return
}
func backtracking(nums []int, path *[]int, res *[][]int, startidx int) {if startidx == len(nums) {return}used := make(map[int]bool)for i:=startidx; i<len(nums); i++ {if used[nums[i]] {continue}// 注意不是对比相邻元素，而是对比当前元素与路径最后一个元素if len(*path) > 0 && nums[i] < (*path)[len(*path) - 1]{continue}*path = append(*path, nums[i])used[nums[i]] = trueif len(*path) > 1 {var copypath = make([]int, len(*path))copy(copypath, *path)*res = append(*res, copypath)}backtracking(nums, path, res, i+1)*path = (*path)[0 : len(*path) - 1]}return
}
46 全排列
func permute(nums []int) [][]int {// 组合问题相比排列问题，递归时候传入的数组不是nums[i+1: ], 而是nums.Remove(nums[i])var path []intvar res [][]intbacktracking(nums, &path, &res)return res
}func backtracking(nums []int, path *[]int, res *[][]int) {if len(nums) == 0 {var copyPath = make([]int, len(*path))copy(copyPath, *path)*res = append(*res, copyPath)return}for i:=0; i<len(nums); i++{*path = append(*path, nums[i])// 新的数组要去除nums[i], 但是要包含其他的元素//在 Go 中，切片操作 nums[a:b] 是合法的，只要满足以下条件：//0 <= a <= b <= len(nums)//nums[a:b] 返回从索引 a 开始到索引 b-1 结束的子切片。//var newNums = make([]int, len(nums) - 1)//copy(newNums, nums[0: i])//copy(newNums[i: ], nums[i+1: ])var newNums []intnewNums = append(newNums, nums[0 : i]...)newNums = append(newNums, nums[i+1: ]...)backtracking(newNums, path, res)*path = (*path)[ : len(*path) - 1]}return
}
// 两个易错点，newnums声明如果放到for循环外面可能出现错误，多次append导致newnums不断累加
// 第二点易错，使用copy函数注意第二个copy dst是newnums[i: ] 而不是newnums, 这样会覆盖第一个copy结果
全排列2
func permuteUnique(nums []int) [][]int {// 组合问题相比排列问题，递归时候传入的数组不是nums[i+1: ], 而是nums.Remove(nums[i])var path []intvar res [][]intbacktracking(nums, &path, &res)return res
}func backtracking(nums []int, path *[]int, res *[][]int) {if len(nums) == 0 {var copyPath = make([]int, len(*path))copy(copyPath, *path)*res = append(*res, copyPath)return}var used = make(map[int]bool)for i:=0; i<len(nums); i++{if used[nums[i]] {continue}used[nums[i]] = true*path = append(*path, nums[i])var newNums []intnewNums = append(newNums, nums[0 : i]...)newNums = append(newNums, nums[i+1: ]...)backtracking(newNums, path, res)*path = (*path)[ : len(*path) - 1]}return
}
// 相比上一题，加了一个used数组保存使用过的元素
