v2ray_simple/utils/algo.go

package utils

//Combinatorics

//func AllSubSets edited from https://github.com/mxschmitt/golang-combinations with MIT License
// All returns all combinations for a given T array.
// This is essentially a powerset of the given set except that the empty set is disregarded.
func AllSubSets[T comparable](set []T) (subsets [][]T) {
	length := uint(len(set))

	// Go through all possible combinations of objects
	// from 1 (only first object in subset) to 2^length (all objects in subset)
	for subsetBits := 1; subsetBits < (1 << length); subsetBits++ {
		var subset []T

		for object := uint(0); object < length; object++ {
			// checks if object is contained in subset
			// by checking if bit 'object' is set in subsetBits
			if (subsetBits>>object)&1 == 1 {
				// add object to subset
				subset = append(subset, set[object])
			}
		}
		// add subset to subsets
		subsets = append(subsets, subset)
	}
	return subsets
}

//AllSubSets 测速有点慢, 我改进一下内存分配,可加速一倍多
func AllSubSets_improve1[T comparable](set []T) (subsets [][]T) {
	length := uint(len(set))
	subsets = make([][]T, 0, length*length)

	for subsetBits := 1; subsetBits < (1 << length); subsetBits++ {
		var subset []T = make([]T, 0, length)

		for object := uint(0); object < length; object++ {
			if (subsetBits>>object)&1 == 1 {
				subset = append(subset, set[object])
			}
		}
		subsets = append(subsets, subset)
	}
	return subsets
}

func DuplicateSlice[T any](a []T) (r []T) {
	r = make([]T, len(a))
	copy(r, a)
	return
}

// TrimSlice 从一个slice中移除一个元素, 会直接改动原slice数据
func TrimSlice[T any](a []T, deleteIndex int) []T {
	j := 0
	for idx, val := range a {
		if idx != deleteIndex {
			a[j] = val
			j++
		}
	}
	return a[:j]
}