Add Duplicate Character Counter in V (#5197)

Author: Azeb-S

archive/v/v/duplicate-character-counter.v

@@ -0,0 +1,36 @@
+import os
+
+fn show_error() {
+	println('Usage: please provide a string')
+}
+
+fn main() {
+	args := os.args[1..] // skip program name
+	if args.len == 0 {
+		show_error()
+		return
+	}
+	input_str := args[0]
+	if input_str.len == 0 {
+		show_error()
+		return
+	}
+
+	mut counts := map[rune]int{}
+	for c in input_str.runes() {
+		counts[c]++
+	}
+
+	mut found := false
+	for c in input_str.runes() {
+		if counts[c] > 1 {
+			println('${c.str()}: ${counts[c]}')
+			counts[c] = 0 // prevent duplicate printing
+			found = true
+		}
+	}
+
+	if !found {
+		println('No duplicate characters')
+	}
+}