sum

algorithm/helper.go

@@ -73,9 +73,15 @@ func UniqueBy[T any, K cmp.Ordered, A ~[]T](arr A, getKey func(item T) K) A {
 	return arr
 }
 
+// Sum 求和
+func Sum[T cmp.Number](arr []T) T {
+	var sum T
+	return Reduce(arr, sum, func(s T, item T) T { return s + item })
+}
+
 // Reduce 对数组中的每个元素按序执行一个提供的 reducer 函数，每一次运行 reducer 会将先前元素的计算结果作为参数传入，
 // 最后将其结果汇总为单个返回值。
-func Reduce[T any, S any](initialValue S, arr []T, reducer func(s S, item T) S) S {
+func Reduce[T any, S any](arr []T, initialValue S, reducer func(s S, item T) S) S {
 	for _, item := range arr {
 		initialValue = reducer(initialValue, item)
 	}

algorithm/helper_test.go

@@ -187,7 +187,7 @@ func TestIsZero(t *testing.T) {
 func TestReduce(t *testing.T) {
 	t.Run("", func(t *testing.T) {
 		var arr = []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
-		var sum = Reduce(0, arr, func(summarize int, item int) int {
+		var sum = Reduce(arr, 0, func(summarize int, item int) int {
 			return summarize + item
 		})
 		assert.Equal(t, sum, 55)
@@ -196,10 +196,16 @@ func TestReduce(t *testing.T) {
 	t.Run("", func(t *testing.T) {
 		var arr = []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
 		var m = hashmap.New[int, struct{}](10)
-		Reduce(m, arr, func(s hashmap.HashMap[int, struct{}], item int) hashmap.HashMap[int, struct{}] {
+		Reduce(arr, m, func(s hashmap.HashMap[int, struct{}], item int) hashmap.HashMap[int, struct{}] {
 			s.Set(item, struct{}{})
 			return s
 		})
 		assert.ElementsMatch(t, m.Keys(), []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
 	})
 }
+
+func TestSum(t *testing.T) {
+	assert.Equal(t, Sum([]int{}), 0)
+	assert.Equal(t, Sum([]int{1, 3, 5, 7, 9}), 25)
+	assert.Equal(t, Sum([]uint32{1, 3, 5, 7, 9}), uint32(25))
+}