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snippets/js/s/string-permutations.md

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+---
+title: String permutations
+type: snippet
+language: javascript
+tags: [string,recursion]
+cover: mac-and-coffee
+dateModified: 2020-11-15T17:13:42+02:00
+---
+
+Generates all permutations of a string (contains duplicates).
+
+- Use recursion.
+- For each letter in the given string, create all the partial permutations for the rest of its letters.
+- Use `Array.prototype.map()` to combine the letter with each partial permutation.
+- Use `Array.prototype.reduce()` to combine all permutations in one array.
+- Base cases are for `String.prototype.length` equal to `2` or `1`.
+- ⚠️ **WARNING**: The execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your environment to hang as it tries to solve all the different combinations.
+
+```js
+const stringPermutations = str => {
+  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
+  return str
+    .split('')
+    .reduce(
+      (acc, letter, i) =>
+        acc.concat(
+          stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(
+            val => letter + val
+          )
+        ),
+      []
+    );
+};
+```
+
+```js
+stringPermutations('abc'); // ['abc', 'acb', 'bac', 'bca', 'cab', 'cba']
+```