Create 1915-number-of-wonderful-substrings.js

Author: everthis

1915-number-of-wonderful-substrings.js

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+/**
+ * @param {string} word
+ * @return {number}
+ */
+const asi = (c) => c.charCodeAt();
+const wonderfulSubstrings = (s) => {
+    let res = 0;
+    let f = Array(2 ** 10).fill(0);
+    f[0] = 1; // count array
+    let cur = res = 0;
+    for (const c of s) {
+        cur ^= 1 << asi(c) - 97; // get Hash (the set bit for a character.), update prefix parity
+        res += f[cur];
+        for (let i = 0; i < 10; i++) { // a ~ j
+            res += f[cur ^ 1 << i]; // 1 << i get Hash
+        }
+        f[cur]++;
+    }
+    return res;
+};