additional improve MetricSnapshots.Builder performance (#985)

Signed-off-by: Andrey Burov <burov4j@yandex.ru>

Author: burov4j

prometheus-metrics-model/src/main/java/io/prometheus/metrics/model/snapshots/MetricSnapshots.java

@@ -3,8 +3,10 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Set;
 import java.util.stream.Stream;
 
 import static io.prometheus.metrics.model.snapshots.PrometheusNaming.prometheusName;
@@ -74,6 +76,7 @@ public static Builder builder() {
     public static class Builder {
 
         private final List<MetricSnapshot> snapshots = new ArrayList<>();
+        private final Set<String> prometheusNames = new HashSet<>();
 
         private Builder() {
         }
@@ -83,19 +86,15 @@ public boolean containsMetricName(String name) {
                 return false;
             }
             String prometheusName = prometheusName(name);
-            for (MetricSnapshot snapshot : snapshots) {
-                if (snapshot.getMetadata().getPrometheusName().equals(prometheusName)) {
-                    return true;
-                }
-            }
-            return false;
+            return prometheusNames.contains(prometheusName);
         }
 
         /**
          * Add a metric snapshot. Call multiple times to add multiple metric snapshots.
          */
         public Builder metricSnapshot(MetricSnapshot snapshot) {
             snapshots.add(snapshot);
+            prometheusNames.add(snapshot.getMetadata().getPrometheusName());
             return this;
         }