go: add «3223. Minimum Length of String After Operations»

URL:	https://leetcode.com/problems/minimum-length-of-string-after-operations/
Signed-off-by: Matej Focko <me@mfocko.xyz>

go/minimum-length-of-string-after-operations.go

@@ -0,0 +1,29 @@
+package main
+
+func minimumLength(s string) int {
+	freqs := make([]int, 26)
+	for _, c := range s {
+		freqs[c-'a']++
+	}
+
+	length := len(s)
+	for _, c := range freqs {
+		if c <= 2 {
+			// cannot remove anything
+			continue
+		}
+
+		// middle character must be kept
+		c--
+
+		// if there's odd count left, there will be one more character kept
+		if c%2 != 0 {
+			c--
+		}
+
+		// rest can be safely removed
+		length -= c
+	}
+
+	return length
+}