tasks a-s

Task/Run-length-encoding/D/run-length-encoding-3.d

@@ -0,0 +1,79 @@
+import std.stdio, std.conv, std.utf, std.array;
+import vlq;
+
+struct RLE { // for utf string
+    ubyte[] encoded;
+
+    RLE encode(const string s) {
+        validate(s); // check if s is well-formed utf, throw if not
+        encoded.length = 0; // reset
+        if (s.length == 0) return this; // empty string
+        string last;
+        VLQ count;
+        for (int i = 0; i < s.length; ) {
+            auto k = s.stride(i);
+            auto ucode = cast(string)s[i .. i + k];
+            if (i == 0) last = ucode;
+            if (ucode == last)
+                count++;
+            else {
+                encoded ~= count.toVLQ ~ cast(ubyte[])last;
+                last = ucode;
+                count = 1;
+            }
+            i += k;
+        }
+        encoded ~= VLQ(count).toVLQ ~ cast(ubyte[])last;
+        return this;
+    }
+
+    int opApply(int delegate(ref ulong c, ref string u) dg) {
+        VLQ count;
+        string ucode;
+
+        for (int i = 0; i < encoded.length; ) {
+            auto k = count.extract(encoded[i .. $]);
+            i += k;
+            if (i >= encoded.length)
+                throw new Exception("not valid encoded string");
+            k = stride(cast(string) encoded[i .. $], 0);
+            if (k == 0xff) // not valid utf code point
+                throw new Exception("not valid encoded string");
+            ucode = cast(string)encoded[i .. i + k].dup;
+            dg(count.value, ucode);
+            i += k;
+        }
+
+        return 0;
+    }
+
+    string toString() {
+        string res;
+        foreach (ref i, s ; this)
+            if (indexOf("0123456789#", s) == -1)
+                res ~= text(i) ~ s;
+            else
+                res ~= text(i) ~ '#' ~ s;
+        return res;
+    }
+
+    string decode() {
+        string res;
+        foreach (ref i, s; this)
+            res ~= replicate(s, cast(uint)i);
+        return res;
+    }
+}
+
+void main() {
+    RLE r;
+    auto s = "尋尋覓覓冷冷清清淒淒慘慘戚戚\nWWWWWWWWWWWWBWWWWWWWWWWW" ~
+             "WBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW\n" ~
+             "11#222##333";
+    auto f = File("display.txt", "w");
+    f.writeln(s);
+    r.encode(s);
+    f.writefln("-----\n%s\n-----\n%s", r, r.decode());
+    auto sEncoded = RLE.init.encode(s).encoded ;
+    assert(s == RLE(sEncoded).decode(), "Not work");
+}