Add substring instance count

Author: dwqs

codewars/201807/substring-instance-count.md

@@ -0,0 +1,80 @@
+
+## Description
+
+Complete the solution so that it returns the number of times the search_text is found within the full_text.
+
+```js
+searchSubstr( fullText, searchText, allowOverlap = true )
+```
+
+so that overlapping solutions are (not) counted. If the searchText is empty, it should return 0.
+
+### Examples
+```js
+searchSubstr('aa_bb_cc_dd_bb_e', 'bb') # should return 2 since bb shows up twice
+searchSubstr('aaabbbcccc', 'bbb') # should return 1
+searchSubstr( 'aaa', 'aa' ) # should return 2
+searchSubstr( 'aaa', '' ) # should return 0
+searchSubstr( 'aaa', 'aa', false ) # should return 1
+```
+
+**Kata's link**: [Return substring instance count](https://www.codewars.com/kata/return-substring-instance-count-2)
+
+## Best Practices
+
+**First:**
+```js
+function searchSubstr(fullText, searchText, allowOverlap) {
+  if(searchText == '') return 0;
+  var re = new RegExp(searchText, 'g');
+  if(allowOverlap) {
+    var count = 0;
+    while(re.exec(fullText)) {count++; re.lastIndex -= searchText.length - 1;}
+    return count;
+  } else return (fullText.match(re) || []).length || 0;
+}
+```
+
+**Second:**
+```js
+function searchSubstr( fullText, searchText, allowOverlap ){
+  if(fullText == "" || searchText == "") return 0;
+  
+  var re = new RegExp(searchText, "g"), count = 0, match;
+  while (match = re.exec(fullText)) {
+    count++;
+    if(allowOverlap) re.lastIndex = match.index+1;
+  }
+  return count;
+}
+```
+
+## My solutions
+```js
+function countOverlap (reg, matched, fullText, searchText) {
+    let count = matched.length;
+    for (let i = 0, l = matched.length; i < l; i++) {
+        const start = fullText.indexOf(matched[0]) + 1;
+        const end = start + searchText.length;
+        const sub = fullText.slice(start, end + 1);
+        
+        if (reg.test(sub)) {
+            count += 1;
+        }
+
+        fullText = fullText.slice(start + searchText.length);
+    }
+    return count;
+}
+
+function searchSubstr( fullText, searchText, allowOverlap = true ){
+    if (!searchText) {
+        return 0;
+    }
+
+    const reg = new RegExp(searchText, 'g');
+    const matched = fullText.match(reg);
+
+    return allowOverlap ? (matched ? countOverlap(reg, matched, fullText, searchText) : 0) : (matched ? matched.length : 0);
+}
+```

readme.md

@@ -7,6 +7,7 @@ Here is my codewars homepage: https://www.codewars.com/users/dwqs.
 
 ## Lists
 ### 2018-07
+* [Return substring instance count](codewars/201807/substring-instance-count.md)
 * [Simple Pig Latin](codewars/201807/simple-pig-latin.md)
 * [Weight for weight](codewars/201807/weight-for-weight.md)
 * [Valid Parentheses](codewars/201807/valid-parentheses.md)