Add solution #408

Author: JoshCrozier

README.md

@@ -396,6 +396,7 @@
 405|[Convert a Number to Hexadecimal](./solutions/0405-convert-a-number-to-hexadecimal.js)|Easy|
 406|[Queue Reconstruction by Height](./solutions/0406-queue-reconstruction-by-height.js)|Medium|
 407|[Trapping Rain Water II](./solutions/0407-trapping-rain-water-ii.js)|Hard|
+408|[Valid Word Abbreviation](./solutions/0408-valid-word-abbreviation.js)|Easy|
 409|[Longest Palindrome](./solutions/0409-longest-palindrome.js)|Easy|
 410|[Split Array Largest Sum](./solutions/0410-split-array-largest-sum.js)|Hard|
 412|[Fizz Buzz](./solutions/0412-fizz-buzz.js)|Easy|

solutions/0408-valid-word-abbreviation.js

@@ -0,0 +1,55 @@
+/**
+ * 408. Valid Word Abbreviation
+ * https://leetcode.com/problems/valid-word-abbreviation/
+ * Difficulty: Easy
+ *
+ * A string can be abbreviated by replacing any number of non-adjacent, non-empty substrings
+ * with their lengths. The lengths should not have leading zeros.
+ *
+ * For example, a string such as "substitution" could be abbreviated as (but not limited to):
+ * - "s10n" ("s ubstitutio n")
+ * - "sub4u4" ("sub stit u tion")
+ * - "12" ("substitution")
+ * - "su3i1u2on" ("su bst i t u ti on")
+ * - "substitution" (no substrings replaced)
+ *
+ * The following are not valid abbreviations:
+ * - "s55n" ("s ubsti tutio n", the replaced substrings are adjacent)
+ * - "s010n" (has leading zeros)
+ * - "s0ubstitution" (replaces an empty substring)
+ *
+ * Given a string word and an abbreviation abbr, return whether the string matches the given
+ * abbreviation.
+ *
+ * A substring is a contiguous non-empty sequence of characters within a string.
+ */
+
+/**
+ * @param {string} word
+ * @param {string} abbr
+ * @return {boolean}
+ */
+var validWordAbbreviation = function(word, abbr) {
+  let wordIndex = 0;
+  let abbrIndex = 0;
+
+  while (wordIndex < word.length && abbrIndex < abbr.length) {
+    if (word[wordIndex] === abbr[abbrIndex]) {
+      wordIndex++;
+      abbrIndex++;
+      continue;
+    }
+
+    if (abbr[abbrIndex] < '0' || abbr[abbrIndex] > '9') return false;
+    if (abbr[abbrIndex] === '0') return false;
+
+    let num = 0;
+    while (abbrIndex < abbr.length && /[0-9]/.test(abbr[abbrIndex])) {
+      num = num * 10 + Number(abbr[abbrIndex]);
+      abbrIndex++;
+    }
+    wordIndex += num;
+  }
+
+  return wordIndex === word.length && abbrIndex === abbr.length;
+};