Create 2156-find-substring-with-given-hash-value.js

Author: everthis

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

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+/**
+ * @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) {
+  let n = s.length;
+  const p_pow = Array(n + 1);
+  p_pow[0] = 1n;
+  power = BigInt(power);
+  let m = BigInt(modulo);
+  for (let i = 1; i < p_pow.length; i++) p_pow[i] = (p_pow[i - 1] * power) % m;
+
+  const val = (ch) => BigInt(ch.charCodeAt(0) - "a".charCodeAt(0));
+  const h = Array(n + 1).fill(0n);
+  for (let i = n - 1; i >= 0; i--)
+    h[i] = (h[i + 1] * power + val(s[i]) + 1n) % m;
+
+  for (let i = 0; i + k - 1 < n; i++) {
+    let cur_h = (h[i] - h[i + k] * p_pow[k]) % m;
+    let temp = (cur_h + m) % m;
+    if (temp == hashValue) {
+      return s.substr(i, k);
+    }
+  }
+  return "";
+};