Data commit

Task/Twelve-statements/Go/twelve-statements.go

@@ -0,0 +1,127 @@
+package main
+
+import "fmt"
+
+// its' not too much more work to check all the permutations concurrently
+var solution = make(chan int)
+var nearMiss = make(chan int)
+var done = make(chan bool)
+
+func main() {
+    // iterate and use the bits as the permutation
+    for i := 0; i < 4096; i++ {
+        go checkPerm(i)
+    }
+    // collect the misses and list them after the complete solution(s)
+    var ms []int
+    for i := 0; i < 4096; {
+        select {
+        case <-done:
+            i++
+        case s := <-solution:
+            print12("solution", s)
+        case m := <-nearMiss:
+            ms = append(ms, m)
+        }
+    }
+    for _, m := range ms {
+        print12("near miss", m)
+    }
+}
+
+func print12(label string, bits int) {
+    fmt.Print(label, ":")
+    for i := 1; i <= 12; i++ {
+        if bits&1 == 1 {
+            fmt.Print(" ", i)
+        }
+        bits >>= 1
+    }
+    fmt.Println()
+}
+
+func checkPerm(tz int) {
+    // closure returns true if tz bit corresponding to
+    // 1-based statement number is 1.
+    ts := func(n uint) bool {
+        return tz>>(n-1)&1 == 1
+    }
+    // variadic closure returns number of statements listed as arguments
+    // which have corresponding tz bit == 1.
+    ntrue := func(xs ...uint) int {
+        nt := 0
+        for _, x := range xs {
+            if ts(x) {
+                nt++
+            }
+        }
+        return nt
+    }
+    // a flag used on repeated calls to test.
+    // set to true when first contradiction is found.
+    // if another is found, this function (checkPerm) can "short circuit"
+    // and return immediately without checking additional statements.
+    var con bool
+    // closure called to test each statement
+    test := func(statement uint, b bool) {
+        switch {
+        case ts(statement) == b:
+        case con:
+            panic("bail")
+        default:
+            con = true
+        }
+    }
+    // short circuit mechanism
+    defer func() {
+        if x := recover(); x != nil {
+            if msg, ok := x.(string); !ok && msg != "bail" {
+                panic(x)
+            }
+        }
+        done <- true
+    }()
+
+    // 1. This is a numbered list of twelve statements.
+    test(1, true)
+
+    // 2. Exactly 3 of the last 6 statements are true.
+    test(2, ntrue(7, 8, 9, 10, 11, 12) == 3)
+
+    // 3. Exactly 2 of the even-numbered statements are true.
+    test(3, ntrue(2, 4, 6, 8, 10, 12) == 2)
+
+    // 4. If statement 5 is true, then statements 6 and 7 are both true.
+    test(4, !ts(5) || ts(6) && ts(7))
+
+    // 5. The 3 preceding statements are all false.
+    test(5, !ts(4) && !ts(3) && !ts(2))
+
+    // 6. Exactly 4 of the odd-numbered statements are true.
+    test(6, ntrue(1, 3, 5, 7, 9, 11) == 4)
+
+    // 7. Either statement 2 or 3 is true, but not both.
+    test(7, ts(2) != ts(3))
+
+    // 8. If statement 7 is true, then 5 and 6 are both true.
+    test(8, !ts(7) || ts(5) && ts(6))
+
+    // 9. Exactly 3 of the first 6 statements are true.
+    test(9, ntrue(1, 2, 3, 4, 5, 6) == 3)
+
+    // 10. The next two statements are both true.
+    test(10, ts(11) && ts(12))
+
+    // 11. Exactly 1 of statements 7, 8 and 9 are true.
+    test(11, ntrue(7, 8, 9) == 1)
+
+    // 12. Exactly 4 of the preceding statements are true.
+    test(12, ntrue(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) == 4)
+
+    // no short circuit? send permutation as either near miss or solution
+    if con {
+        nearMiss <- tz
+    } else {
+        solution <- tz
+    }
+}