5: palindromic-substrings

Author: whewchews

palindromic-substrings/whewchews.ts

@@ -0,0 +1,35 @@
+function countSubstrings(s: string): number {
+  // SC: O(N^2)
+  const dict: Map<string, boolean> = new Map();
+  const n = s.length;
+
+  // TC: O(N^2)
+  for (let start = 0; start < n; start++) {
+    for (let end = start; end >= 0; end--) {
+      if (start === end) {
+        dict.set(`${start}:${end}`, true);
+      } else if (start + 1 === end) {
+        dict.set(`${start}:${end}`, s[start] === s[end]);
+      } else {
+        const flag = s[start] === s[end];
+        const mid = dict.get(`${start + 1}:${end - 1}`);
+        dict.set(`${start}:${end}`, flag && mid);
+      }
+    }
+  }
+
+  let cnt = 0;
+
+  // TC: O(N^2)
+  // SC: O(1)
+  for (const v of dict.values()) {
+    if (v) {
+      cnt++;
+    }
+  }
+
+  return cnt;
+}
+
+// TC: O(N^2)
+// SC: O(N^2)