add new solutions

solutions/0/q5/solution.go

@@ -0,0 +1,37 @@
+package q5
+
+// Note: Although it can be done in O(N) with, e.g., Manacher's algorithm, the
+// input size is small enough to brute-force.
+
+func expand(s string, l, r int) (int, int) {
+	for l > 0 && r < len(s)-1 && s[l-1] == s[r+1] {
+		l--
+		r++
+	}
+	return l, r
+}
+
+func longestPalindrome(s string) string {
+	maxLen, mL, mR := 0, 0, 0
+
+	for c := range len(s) {
+		l, r := expand(s, c, c)
+		len_ := r - l + 1
+		if len_ > maxLen {
+			maxLen, mL, mR = len_, l, r
+		}
+	}
+
+	for c := range len(s) - 1 {
+		if s[c] == s[c+1] {
+			l, r := expand(s, c, c+1)
+			len_ := r - l + 1
+			if len_ > maxLen {
+				maxLen, mL, mR = len_, l, r
+			}
+		}
+	}
+	return s[mL : mR+1]
+}
+
+var _ = longestPalindrome