Add: Exercise 392. Is Subsequence

Author: BlackBeast593

392-is-subsequence/README.md

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+# 392. Is Subsequence
+Given two strings `s` and `t`, return `true` if `s` is a subsequence of `t`, or `false` otherwise.
+
+A subsequence of a string is a new string that is formed from the original string by deleting some
+(can be none) of the characters without disturbing the relative positions of the remaining
+characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
+
+## Examples
+
+### Example 1:
+Input: `s` = "abc", `t` = "ahbgdc"
+Output: `true`
+
+### Example 2:
+Input: `s` = "axc", `t` = "ahbgdc"
+Output: `false`
+
+## Constraints
+- 0 <= `s.length` <= 100
+- 0 <= `t.length` <= 10^4
+- `s` and `t` consist only of lowercase English letters.
+
+## Follow up
+Suppose there are lots of incoming `s`, say `s1`, `s2`, ..., `sk` where `k` >= 10^9, and you want to
+check one by one to see if `t` has its subsequence. In this scenario, how would you change your
+code?

392-is-subsequence/index.js

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+/**
+ * Determines if `s` is a subsequence of `t`. A subsequence is formed by deleting some or no 
+ * elements from a string without changing the order of the remaining elements. This function 
+ * iterates through `t` and compares it with `s`, increasing a pointer for each match. 
+ * If all characters of `s` are found in sequence in `t`, `s` is a subsequence of `t`.
+ * 
+ * @param {string} s - String to check as a subsequence.
+ * @param {string} t - String to be checked against.
+ * @return {boolean} - True if `s` is a subsequence of `t`, false otherwise.
+ */
+
+var isSubsequence = function(s, t) {
+    // Traverse t and advance i when s[i] is found
+    let i = 0 // Index for iterate over t
+    let j = 0 // Index for iterate over s
+
+    // Edge case
+    if (s.length > t.length) {
+        return false
+    }
+
+    while (i < t.length && j < s.length) {
+        if (s[j] === t[i]) {
+            j++
+        }
+        i++
+    }
+
+    return j === s.length
+};
+
+module.exports = isSubsequence

392-is-subsequence/package.json

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+{
+  "name": "392-is-subsequence",
+  "version": "1.0.0",
+  "description": "Given two strings `s` and `t`, return `true` if `s` is a subsequence of `t`, or `false` otherwise.",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js",
+    "debug": "node --inspect-brk index.js",
+    "test": "node test.js"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC"
+}

392-is-subsequence/test.js

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+const assert = require('assert')
+const isSubsequence = require('./index')
+
+const tt = [
+    {
+        s: 'abc',
+        t: 'ahbgdc',
+        expected: true,
+    },
+    {
+        s: 'axc',
+        t: 'ahbgdc',
+        expected: false,
+    }
+]
+
+for (const t of tt) {
+    assert.strict.equal(isSubsequence(t.s, t.t), t.expected)
+}