Add substring count/indexes

snippets/countSubstrings.md

@@ -0,0 +1,27 @@
+---
+title: countSubstrings
+tags: string,algorithm,beginner
+---
+
+Counts the occurences of a substring in a given string.
+
+- Use `Array.prototype.indexOf()` to look for `searchValue` in `str`.
+- Increment a counter if the value is found and update the index, `i`.
+- Use a `while` loop that will return as soon as the value returned from `Array.prototype.indexOf()` is `-1`.
+
+```js
+const countSubstrings = (str, searchValue) => {
+  let count = 0,
+    i = 0;
+  while (true) {
+    const r = str.indexOf(searchValue, i);
+    if (r !== -1) [count, i] = [count + 1, r + 1];
+    else return count;
+  }
+};
+```
+
+```js
+countSubstrings('tiktok tok tok tik tok tik', 'tik'); // 3
+countSubstrings('tutut tut tut', 'tut'); // 4
+```

snippets/indexOfSubstrings.md

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+---
+title: indexOfSubstrings
+tags: string,algorithm,generator,intermediate
+---
+
+Finds all the indexes of a substring in a given string.
+
+- Use `Array.prototype.indexOf()` to look for `searchValue` in `str`.
+- Use `yield` to return the index if the value is found and update the index, `i`.
+- Use a `while` loop that will terminate the generator as soon as the value returned from `Array.prototype.indexOf()` is `-1`.
+
+```js
+const indexOfSubstrings = function* (str, searchValue) {
+  let i = 0;
+  while (true) {
+    const r = str.indexOf(searchValue, i);
+    if (r !== -1) {
+      yield r;
+      i = r + 1;
+    } else return;
+  }
+};
+```
+
+```js
+[...indexOfSubstrings('tiktok tok tok tik tok tik', 'tik')]; // [0, 15, 23]
+[...indexOfSubstrings('tutut tut tut', 'tut')]; // [0, 2, 6, 10]
+[...indexOfSubstrings('hello', 'hi')]; // []
+```