Data commit

Task/Run-length-encoding/Go/run-length-encoding.go

@@ -0,0 +1,71 @@
+package main
+
+import "fmt"
+
+// encoding scheme:
+// encode to byte array
+// byte value < 26 means single character: byte value + 'A'
+// byte value 26..255 means (byte value - 24) copies of next byte
+func rllEncode(s string) (r []byte) {
+    if s == "" {
+        return
+    }
+    c := s[0]
+    if c < 'A' || c > 'Z' {
+        panic("invalid")
+    }
+    nc := byte(1)
+    for i := 1; i < len(s); i++ {
+        d := s[i]
+        switch {
+        case d != c:
+        case nc < (255 - 24):
+            nc++
+            continue
+        }
+        if nc > 1 {
+            r = append(r, nc+24)
+        }
+        r = append(r, c-'A')
+        if d < 'A' || d > 'Z' {
+            panic("invalid")
+        }
+        c = d
+        nc = 1
+    }
+    if nc > 1 {
+        r = append(r, nc+24)
+    }
+    r = append(r, c-'A')
+    return
+}
+
+func main() {
+    s := "WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW"
+    fmt.Println("source: ", len(s), "bytes:", s)
+    e := rllEncode(s)
+    fmt.Println("encoded:", len(e), "bytes:", e)
+    d := rllDecode(e)
+    fmt.Println("decoded:", len(d), "bytes:", d)
+    fmt.Println("decoded = source:", d == s)
+}
+
+func rllDecode(e []byte) string {
+    var c byte
+    var d []byte
+    for i := 0; i < len(e); i++ {
+        b := e[i]
+        if b < 26 {
+            c = 1
+        } else {
+            c = b - 24
+            i++
+            b = e[i]
+        }
+        for c > 0 {
+            d = append(d, b+'A')
+            c--
+        }
+    }
+    return string(d)
+}