Add solution #2156

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,781 LeetCode solutions in JavaScript
+# 1,782 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -1651,6 +1651,7 @@
 2151|[Maximum Good People Based on Statements](./solutions/2151-maximum-good-people-based-on-statements.js)|Hard|
 2154|[Keep Multiplying Found Values by Two](./solutions/2154-keep-multiplying-found-values-by-two.js)|Easy|
 2155|[All Divisions With the Highest Score of a Binary Array](./solutions/2155-all-divisions-with-the-highest-score-of-a-binary-array.js)|Medium|
+2156|[Find Substring With Given Hash Value](./solutions/2156-find-substring-with-given-hash-value.js)|Hard|
 2161|[Partition Array According to Given Pivot](./solutions/2161-partition-array-according-to-given-pivot.js)|Medium|
 2176|[Count Equal and Divisible Pairs in an Array](./solutions/2176-count-equal-and-divisible-pairs-in-an-array.js)|Easy|
 2179|[Count Good Triplets in an Array](./solutions/2179-count-good-triplets-in-an-array.js)|Hard|

solutions/2156-find-substring-with-given-hash-value.js

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+/**
+ * 2156. Find Substring With Given Hash Value
+ * https://leetcode.com/problems/find-substring-with-given-hash-value/
+ * Difficulty: Hard
+ *
+ * The hash of a 0-indexed string s of length k, given integers p and m, is computed using
+ * the following function:
+ * - hash(s, p, m) = (val(s[0]) * p0 + val(s[1]) * p1 + ... + val(s[k-1]) * pk-1) mod m.
+ *
+ * Where val(s[i]) represents the index of s[i] in the alphabet from val('a') = 1 to val('z') = 26.
+ *
+ * You are given a string s and the integers power, modulo, k, and hashValue. Return sub, the
+ * first substring of s of length k such that hash(sub, power, modulo) == hashValue.
+ *
+ * The test cases will be generated such that an answer always exists.
+ *
+ * A substring is a contiguous non-empty sequence of characters within a string.
+ */
+
+/**
+* @param {string} s
+* @param {number} power
+* @param {number} modulo
+* @param {number} k
+* @param {number} hashValue
+* @return {string}
+*/
+var subStrHash = function(s, power, modulo, k, hashValue) {
+  power = BigInt(power);
+  modulo = BigInt(modulo);
+  hashValue = BigInt(hashValue);
+
+  const powers = new Array(k);
+  powers[0] = 1n;
+  for (let i = 1; i < k; i++) {
+    powers[i] = (powers[i - 1] * power) % modulo;
+  }
+
+  for (let start = 0; start <= s.length - k; start++) {
+    let hash = 0n;
+    for (let i = 0; i < k; i++) {
+      const charVal = BigInt(s.charCodeAt(start + i) - 'a'.charCodeAt(0) + 1);
+      hash = (hash + charVal * powers[i]) % modulo;
+    }
+    if (hash === hashValue) {
+      return s.substring(start, start + k);
+    }
+  }
+
+  return '';
+};