update

copypasta/bits.go

@@ -93,6 +93,8 @@ func bitsCollection() {
 	// ^n+1 = (-1-n)+1 = -n
 	lowbit := func(n int64) int64 { return n & -n }
 
+	isPow2 := func(x int64) bool { return x > 0 || x&(x-1) == 0 }
+
 	bits31 := func(n int) []byte {
 		bits := make([]byte, 31)
 		for i := range bits {
@@ -110,7 +112,7 @@ func bitsCollection() {
 		return
 	}
 
-	_ = []interface{}{lowbit, bits31, _bits31, _bits32, digitSum}
+	_ = []interface{}{lowbit, isPow2, bits31, _bits31, _bits32, digitSum}
 }
 
 // https://halfrost.com/go_s2_de_bruijn/

copypasta/dp.go

@@ -572,6 +572,10 @@ func dpCollections() {
 	todo LC691  https://leetcode-cn.com/problems/stickers-to-spell-word/
 	     LC1125 https://leetcode-cn.com/problems/smallest-sufficient-team/
 	     LC943  https://leetcode-cn.com/problems/find-the-shortest-superstring/
+
+	枚举子集，复杂度 O(3^n)
+		dp[s] = min(valid dp[s^sub]) + 1
+		todo LC1494/双周赛29D https://leetcode-cn.com/problems/parallel-courses-ii/
 	todo 汉密尔顿路径/回路 Hamiltonian path
 	*/
 

copypasta/search.go

@@ -351,9 +351,34 @@ func loopCollection() {
 	loopSubset := func(n, subset int) {
 		sub := subset
 		for ok := true; ok; ok = sub != subset {
-			// do(sub)
+			// do(sub)...
+
 			sub = (sub - 1) & subset
 		}
+
+		{
+			// 非空子集
+			for sub := subset; sub > 0; sub = (sub - 1) & subset {
+				// do(sub)...
+
+			}
+		}
+
+		{
+			// 真子集
+			for sub := (subset - 1) & subset; sub != subset; sub = (sub - 1) & subset {
+				// do(sub)...
+
+			}
+		}
+
+		{
+			// 非空真子集
+			for sub := (subset - 1) & subset; sub > 0; sub = (sub - 1) & subset {
+				// do(sub)...
+
+			}
+		}
 	}
 
 	// 枚举大小为 n 的集合的大小为 k 的子集（按字典序）