add a simple hash function

Author: hadis98

hash_table/hash_table.js

@@ -0,0 +1,48 @@
+function hash(key, arayLen) {
+    let total = 0;
+    for (let char of key) {
+        //map "a" to 1,"b" to 2,"c" to 3,etc.
+        let value = char.charCodeAt(0) - 96;
+        total = (total + value) % arayLen;
+    }
+    return total;
+}
+console.log('without prime hash: ');
+console.log(hash("pink", 10));
+console.log(hash("blue", 10));
+console.log(hash("orangered", 10));
+console.log(hash("cyan", 10));
+
+/*
+problems of this hash function:
+1.only hashes string
+2.not constant time - linear in key length
+3.could be a little more random
+*/
+
+
+function prime_hash(key, arayLen) {
+    let total = 0;
+    let WEIRD_PRIME = 31;
+    for (let i = 0; i < Math.min(key.length, 100); i++) {
+        let char = key[i];
+        let value = char.charCodeAt(0) - 96;
+        total = (total * WEIRD_PRIME + value) % arayLen;
+    }
+
+    return total;
+}
+console.log('with prime hash: ');
+console.log(prime_hash("pink", 13));
+console.log(prime_hash("blue", 13));
+console.log(prime_hash("orangered", 13));
+console.log(prime_hash("cyan", 13));
+
+
+/*
+prime number in the hash is helpful in spreading out the keys more uniformly
+
+it's also helpful if the array that you're putting values into has a prime length
+
+so hash functions use prime numbers
+*/