diff --git a/lib/the_flx.dart b/lib/the_flx.dart
index 48eba5e..5c209e5 100644
--- a/lib/the_flx.dart
+++ b/lib/the_flx.dart
@@ -1,11 +1,50 @@
+import 'dart:math';
+
+class Util {
+  static dictSet(Map<int, List<Result>> result, int? key, List<Result> val) {
+    if (key == null) return;
+
+    if (!result.containsKey(key)) {
+      result[key] = val;
+    }
+
+    result[key] = val;
+  }
+
+  static List<T>? dictGet<T>(Map<int, List<T>> dict, int? key) {
+    if (key == null) return null;
+
+    if (!dict.containsKey(key)) return null;
+
+    return dict[key];
+  }
+
+  static void dictInsert(Map<int, List<int>> result, int? key, int val) {
+    if (key == null) return;
+
+    if (!result.containsKey(key)) result[key] = [];
+
+    List<int>? lst = result[key];
+
+    if (lst == null) return;
+
+    lst.insert(0, val);
+  }
+}
+
 class Result {
-  int score = 0;
-  List<int> indicies = [];
+  List<int> indices = [];
+  int score;
+  int tail;
+
+  Result(this.indices, this.score, this.tail);
 }
 
 class Flx {
   /* Variables */
 
+  static const int int32Min = -2147483648; /* -(2^31) */
+
   static List<int> wordSeparators = [
     toChar(' '),
     toChar('-'),
@@ -39,6 +78,12 @@ class Flx {
     return String.fromCharCodes([ch]).toUpperCase().codeUnitAt(0);
   }
 
+  /// Convert [ch] to lowercase char.
+  static int? toLowerCase(int? ch) {
+    if (ch == null) return null;
+    return String.fromCharCodes([ch]).toLowerCase().codeUnitAt(0);
+  }
+
   /// Check if [ch] is an uppercase character.
   ///
   /// Return true if the [ch] is a Capital character.
@@ -69,8 +114,302 @@ class Flx {
     return vec;
   }
 
+  /// Return hash-table for string where keys are characters.
+  /// Value is a sorted list of indexes for character occurrences.
+  static Map<int, List<int>>? getHashForString(String? str) {
+    if (str == null) return null;
+
+    Map<int, List<int>> result = {};
+
+    int strLen = str.length;
+    int index = strLen - 1;
+    int? ch;
+    int? downCh;
+
+    while (0 <= index) {
+      ch = toChar(str[index]);
+
+      if (capital(ch)) {
+        Util.dictInsert(result, ch, index);
+
+        downCh = toLowerCase(ch);
+      } else {
+        downCh = ch;
+      }
+
+      Util.dictInsert(result, downCh, index);
+
+      --index;
+    }
+
+    return result;
+  }
+
+  /// Generate the heatmap vector of string.
+  static List<int>? getHeatmapStr(String? str, int? groupSeparator) {
+    if (str == null) return null;
+
+    List<int> scores = [];
+    int strLen = str.length;
+    int strLastIndex = strLen - 1;
+
+    for (int i = 0; i < strLen; ++i) {
+      scores.add(defaultScore);
+    }
+
+    int penaltyLead = toChar('.');
+
+    List<int> inner = [-1, 0];
+    List<List<int>> groupAlist = [inner];
+
+    // final char bonus
+    scores[strLastIndex] += 1;
+
+    // Establish baseline mapping
+    int? lastCh;
+    int groupWordCount = 0;
+
+    for (int index = 0; index < str.length; ++index) {
+      int ch = toChar(str[index]);
+
+      // before we find any words, all separaters are
+      // considered words of length 1.  This is so "foo/__ab"
+      // gets penalized compared to "foo/ab".
+      int? effectiveLastChar = ((groupWordCount == 0) ? null : lastCh);
+
+      if (boundary(effectiveLastChar, ch)) {
+        groupAlist[0].insert(2, index);
+      }
+
+      if (!word(lastCh) && word(ch)) {
+        ++groupWordCount;
+      }
+
+      // ++++ -45 penalize extension
+      if (lastCh != null && lastCh == penaltyLead) {
+        scores[index] += -45;
+      }
+
+      if (groupSeparator != null && groupSeparator == ch) {
+        groupAlist[0][1] = groupWordCount;
+        groupWordCount = 0;
+        groupAlist.insert(0, [index, groupWordCount]);
+      }
+
+      if (index == strLastIndex) {
+        groupAlist[0][1] = groupWordCount;
+      } else {
+        lastCh = ch;
+      }
+    }
+
+    int groupCount = groupAlist.length;
+    int separatorCount = groupCount - 1;
+
+    // ++++ slash group-count penalty
+    if (separatorCount != 0) {
+      incVec(scores, groupCount * -2, null, null);
+    }
+
+    int index2 = separatorCount;
+    int? lastGroupLimit;
+    bool basepathFound = false;
+
+    // score each group further
+    for (List<int> group in groupAlist) {
+      int groupStart = group[0];
+      int wordCount = group[1];
+      // this is the number of effective word groups
+      int wordsLength = group.length - 2;
+      bool basepathP = false;
+
+      if (wordsLength != 0 && !basepathFound) {
+        basepathFound = true;
+        basepathP = true;
+      }
+
+      int num;
+      if (basepathP) {
+        // ++++ basepath separator-count boosts
+        int boosts = 0;
+        if (separatorCount > 1) boosts = separatorCount - 1;
+        // ++++ basepath word count penalty
+        int penalty = -wordCount;
+        num = 35 + boosts + penalty;
+      }
+      // ++++ non-basepath penalties
+      else {
+        if (index2 == 0) {
+          num = -3;
+        } else {
+          num = -5 + (index2 - 1);
+        }
+      }
+
+      incVec(scores, num, groupStart + 1, lastGroupLimit);
+
+      List<int> cddrGroup = List.from(group); // clone it
+      cddrGroup.removeAt(0);
+      cddrGroup.removeAt(0);
+
+      int wordIndex = wordsLength - 1;
+      int lastWord = (lastGroupLimit != null) ? lastGroupLimit : strLen;
+
+      for (int word in cddrGroup) {
+        // ++++  beg word bonus AND
+        scores[word] += 85;
+
+        int index3 = word;
+        int charI = 0;
+
+        while (index3 < lastWord) {
+          scores[index3] += (-3 * wordIndex) - // ++++ word order penalty
+              charI; // ++++ char order penalty
+          ++charI;
+
+          ++index3;
+        }
+
+        lastWord = word;
+        --wordIndex;
+      }
+
+      lastGroupLimit = groupStart + 1;
+      --index2;
+    }
+
+    return scores;
+  }
+
+  /// Return sublist bigger than [val] from sorted [sorted-list].
+  static List<int>? biggerSublist(List<int>? sortedList, int? val) {
+    if (sortedList == null) return null;
+
+    List<int> result = [];
+
+    if (val != null) {
+      for (var sub in sortedList) {
+        if (sub > val) {
+          result.add(sub);
+        }
+      }
+    } else {
+      for (var sub in sortedList) {
+        result.add(sub);
+      }
+    }
+
+    return result;
+  }
+
+  /// Recursively compute the best match for a string, passed as STR-INFO and
+  /// HEATMAP, according to QUERY.
+  static void findBestMatch(
+      List<Result> imatch,
+      Map<int, List<int>> strInfo,
+      List<int> heatmap,
+      int? greaterThan,
+      String query,
+      int queryLength,
+      int qIndex,
+      Map<int, List<Result>> matchCache) {
+    int? greaterNum = (greaterThan != null) ? greaterThan : 0;
+    int? hashKey = qIndex + (greaterNum * queryLength);
+    List<Result>? hashValue = Util.dictGet(matchCache, hashKey);
+
+    if (hashValue != null) {
+      // Process matchCache here
+      imatch.clear();
+      for (var val in hashValue) {
+        imatch.add(val);
+      }
+    } else {
+      int uchar = toChar(query[qIndex]);
+      List<int>? sortedList = Util.dictGet(strInfo, uchar);
+      List<int>? indexes = biggerSublist(sortedList, greaterThan);
+      if (indexes == null) {
+        return;
+      }
+      int tempScore;
+      int bestScore = int32Min;
+
+      if (qIndex >= queryLength - 1) {
+        // At the tail end of the recursion, simply generate all possible
+        // matches with their scores and return the list to parent.
+        for (int index in indexes) {
+          List<int> indices = [];
+          indices.add(index);
+          imatch.add(Result(indices, heatmap[index], 0));
+        }
+      } else {
+        for (int index in indexes) {
+          List<Result> elemGroup = [];
+          findBestMatch(elemGroup, Map.from(strInfo), List.from(heatmap), index,
+              query, queryLength, qIndex + 1, matchCache);
+
+          for (Result elem in elemGroup) {
+            int caar = elem.indices[0];
+            int cadr = elem.score;
+            int cddr = elem.tail;
+
+            if ((caar - 1) == index) {
+              tempScore = cadr +
+                  heatmap[index] +
+                  (min(cddr, 3) * 15) + // boost contiguous matches
+                  60;
+            } else {
+              tempScore = cadr + heatmap[index];
+            }
+
+            // We only care about the optimal match, so only forward the match
+            // with the best score to parent
+            if (tempScore > bestScore) {
+              bestScore = tempScore;
+
+              imatch.clear();
+              List<int> indices = List.from(elem.indices);
+              indices.insert(0, index);
+              int tail = 0;
+              if ((caar - 1) == index) tail = cddr + 1;
+              imatch.add(Result(indices, tempScore, tail));
+            }
+          }
+        }
+      }
+
+      // Calls are cached to avoid exponential time complexity
+      Util.dictSet(matchCache, hashKey, List.from(imatch));
+    }
+  }
+
   /// Return best score matching [query] against [str].
-  static Result? score(String str, String query) {
-    return null;
+  static Result? score(String? str, String? query) {
+    if (str == null || query == null) return null;
+    if (str == '' || query == '') return null;
+
+    Map<int, List<int>>? strInfo = getHashForString(str);
+    if (strInfo == null) return null;
+
+    List<int>? heatmap = getHeatmapStr(str, null);
+    if (heatmap == null) return null;
+
+    int queryLength = query.length;
+    bool fullMatchBoost = (1 < queryLength) && (queryLength < 5);
+    Map<int, List<Result>> matchCache = {};
+    List<Result> optimalMatch = [];
+
+    findBestMatch(optimalMatch, strInfo, heatmap, null, query, queryLength, 0,
+        matchCache);
+
+    if (optimalMatch.isEmpty) return null;
+
+    Result result1 = optimalMatch[0];
+    int caar = result1.indices.length;
+
+    if (fullMatchBoost && caar == str.length) {
+      result1.score += 10000;
+    }
+
+    return result1;
   }
 }
diff --git a/test/the_flx_test.dart b/test/the_flx_test.dart
index 5092cf8..54abe8a 100644
--- a/test/the_flx_test.dart
+++ b/test/the_flx_test.dart
@@ -13,4 +13,51 @@ void main() {
     expect(Flx.incVec([1, 2, 3], 1, null, null), [2, 3, 4]);
     expect(Flx.incVec([1, 2, 3], 1, 1, null), [1, 3, 4]);
   });
+
+  test('test getHashForString', () {
+    expect(Flx.getHashForString("switch-to-buffer"), {
+      114: [15],
+      101: [14],
+      102: [12, 13],
+      117: [11],
+      98: [10],
+      45: [6, 9],
+      111: [8],
+      116: [3, 7],
+      104: [5],
+      99: [4],
+      105: [2],
+      119: [1],
+      115: [0]
+    });
+  });
+
+  test('test biggerSublist 1', () {
+    expect(Flx.biggerSublist([1, 2, 3, 4], null), [1, 2, 3, 4]);
+  });
+
+  test('test biggerSublist 2', () {
+    expect(Flx.biggerSublist([1, 2, 3, 4], 2), [3, 4]);
+  });
+
+  test('test score `switch-to-buffer`', () {
+    Result? result = Flx.score("switch-to-buffer", "stb");
+    expect(result?.indices, [0, 7, 10]);
+    expect(result?.score, 237);
+    expect(result?.tail, 0);
+  });
+
+  test('test score `TestSomeFunctionExterme`', () {
+    Result? result = Flx.score("TestSomeFunctionExterme", "met");
+    expect(result?.indices, [6, 16, 18]);
+    expect(result?.score, 57);
+    expect(result?.tail, 0);
+  });
+
+  test('test score `MetaX_Version`', () {
+    Result? result = Flx.score("MetaX_Version", "met");
+    expect(result?.indices, [0, 1, 2]);
+    expect(result?.score, 211);
+    expect(result?.tail, 2);
+  });
 }