Palindromic Substrings solution

Author: kim-young

palindromic-substrings/kimyoung.js

@@ -0,0 +1,29 @@
+var countSubstrings = function (s) {
+  let result = 0;
+  for (let i = 0; i < s.length; i++) {
+    let left = i,
+      right = i; // odd length substrings
+    helper(s, left, right);
+
+    (left = i), (right = i + 1); // even length substrings
+    helper(s, left, right);
+  }
+  function helper(s, l, r) {
+    // increment result and keep expanding left and right, while left and right indexes are within range and they're equal
+    while (l >= 0 && r <= s.length && s[l] === s[r]) {
+      result++;
+      l--;
+      r++;
+    }
+  }
+  return result;
+};
+
+// test cases
+console.log(countSubstrings("abc")); // 3
+console.log(countSubstrings("aaa")); // 6
+console.log(countSubstrings("a")); // 1
+console.log(countSubstrings("")); // 0
+
+// space - O(1) - constant variable `result`
+// time - O(n^2) - iterating through the string and expanding both ways