diff --git a/src/main/java/cn/nextop/rxjava/share/practices/Practice1.java b/src/main/java/cn/nextop/rxjava/share/practices/Practice1.java
index b432fea..376cb42 100644
--- a/src/main/java/cn/nextop/rxjava/share/practices/Practice1.java
+++ b/src/main/java/cn/nextop/rxjava/share/practices/Practice1.java
@@ -19,6 +19,10 @@
 import cn.nextop.rxjava.share.util.type.Tuple2;
 import io.reactivex.Observable;
 
+import static cn.nextop.rxjava.share.util.Tuples.of;
+import static io.reactivex.Observable.range;
+import static java.lang.Integer.MAX_VALUE;
+
 /**
  * @author Baoyi Chen
  */
@@ -29,7 +33,7 @@ public class Practice1 {
      * 参数 Observable["a","b","c"]
      * 返回值 Observable[(1, "a"), (2, "b"), (3, "c")] 注意index从1开始
      */
-    public Observable<Tuple2<Integer, String>> indexable(Observable<String> observable) {
-        throw new UnsupportedOperationException("implementation");
+    public Observable<Tuple2<Integer, String>> indexable(Observable<String> ob) {
+        return ob.zipWith(range(1, MAX_VALUE), (i, s) -> of(s, i));
     }
 }
diff --git a/src/main/java/cn/nextop/rxjava/share/practices/Practice2.java b/src/main/java/cn/nextop/rxjava/share/practices/Practice2.java
index 08c7dcd..363c0b4 100644
--- a/src/main/java/cn/nextop/rxjava/share/practices/Practice2.java
+++ b/src/main/java/cn/nextop/rxjava/share/practices/Practice2.java
@@ -21,8 +21,11 @@
 import io.reactivex.Observable;
 import io.reactivex.Single;
 
+import java.util.HashMap;
 import java.util.Map;
 
+import static cn.nextop.rxjava.share.util.Tuples.of;
+
 /**
  * @author Baoyi Chen
  */
@@ -34,7 +37,7 @@ public class Practice2 {
      * 返回: Observable[("a", 2), ("b", 1), ("c", 2)]
      */
     public Observable<Tuple2<String, Integer>> wordCount1(Observable<String> words) {
-        throw new UnsupportedOperationException("implementation");
+        return words.groupBy(e -> e).flatMap(e -> e.count().map(x -> of(e.getKey(), x.intValue())).toObservable());
     }
 
     /*
@@ -43,7 +46,9 @@ public Observable<Tuple2<String, Integer>> wordCount1(Observable<String> words)
      * 返回: Single[Map{a=2, b=1, c=2}]
      */
     public Single<Map<String, Integer>> wordCount2(Observable<String> words) {
-        throw new UnsupportedOperationException("implementation");
+        return words.reduceWith(() -> new HashMap<String, Integer>(), (a, b) -> {
+	    if (a.containsKey(b)) a.put(b, a.get(b) + 1); else a.put(b, 1); return a;
+	});
     }
 
 }
diff --git a/src/main/java/cn/nextop/rxjava/share/practices/Practice3.java b/src/main/java/cn/nextop/rxjava/share/practices/Practice3.java
index a43bd78..12d90e1 100644
--- a/src/main/java/cn/nextop/rxjava/share/practices/Practice3.java
+++ b/src/main/java/cn/nextop/rxjava/share/practices/Practice3.java
@@ -19,6 +19,10 @@
 import io.reactivex.Maybe;
 import io.reactivex.Observable;
 
+import static io.reactivex.Observable.empty;
+import static io.reactivex.Observable.just;
+import static io.reactivex.Observable.merge;
+
 /**
  * @author Baoyi Chen
  */
@@ -28,7 +32,7 @@ public class Practice3 {
      * 根据iterate的结果求和
      */
     public Maybe<Integer> sum(Observable<Node> observable) {
-        throw new UnsupportedOperationException("implementation");
+        return iterate(observable).reduce((x, y) -> x + y);
     }
 
     /*
@@ -42,7 +46,11 @@ public Maybe<Integer> sum(Observable<Node> observable) {
      * return Observable[4, 3, 6, 7, 5] 顺序无关
      */
     public Observable<Integer> iterate(Observable<Node> observable) {
-        throw new UnsupportedOperationException("implementation");
+        return observable.flatMap(n -> {
+            Observable<Integer> left = n.left == null ? empty() : iterate(just(n.left));
+            Observable<Integer> right = n.right == null ? empty() : iterate(just(n.right));
+            return merge(left, right, just(n.value));
+        });
     }
 
     public static class Node {
diff --git a/src/main/java/cn/nextop/rxjava/share/practices/Practice4.java b/src/main/java/cn/nextop/rxjava/share/practices/Practice4.java
index 33a5804..b42f059 100644
--- a/src/main/java/cn/nextop/rxjava/share/practices/Practice4.java
+++ b/src/main/java/cn/nextop/rxjava/share/practices/Practice4.java
@@ -19,6 +19,8 @@
 
 import io.reactivex.Observable;
 
+import static io.reactivex.Observable.just;
+import static io.reactivex.schedulers.Schedulers.newThread;
 
 /**
  * @author Baoyi Chen
@@ -43,8 +45,8 @@ public class Practice4 {
      *                                                         ---------------
      *
      */
-    public Observable<String> runInMultiThread(Observable<String> observable) {
-        throw new UnsupportedOperationException("implementation");
+    public Observable<String> runInMultiThread(Observable<String> ob) {
+        return ob.flatMap(e -> just(e).subscribeOn(newThread()));
     }
 
 }
diff --git a/src/main/java/cn/nextop/rxjava/share/practices/Practice5.java b/src/main/java/cn/nextop/rxjava/share/practices/Practice5.java
index 1193642..40e8cb2 100644
--- a/src/main/java/cn/nextop/rxjava/share/practices/Practice5.java
+++ b/src/main/java/cn/nextop/rxjava/share/practices/Practice5.java
@@ -18,12 +18,17 @@
 
 import io.reactivex.Maybe;
 import io.reactivex.Observable;
+import io.reactivex.ObservableEmitter;
 import io.reactivex.Single;
 
 import java.util.List;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Predicate;
 
+import static cn.nextop.rxjava.share.util.Tuples.of;
+import static io.reactivex.Observable.*;
+import static java.lang.Integer.MAX_VALUE;
+
 /**
  * @author Baoyi Chen
  */
@@ -35,7 +40,7 @@ public class Practice5 {
      * return: Single[3]
      */
     public Single<Long> count(Observable<String> source) {
-        throw new UnsupportedOperationException("implementation");
+        return source.reduce(0L, (a, b) -> a + 1);
     }
 
     /*
@@ -44,7 +49,7 @@ public Single<Long> count(Observable<String> source) {
      * return: Observable["a", "b", "c","b", "c", "d"]
      */
     public Observable<String> convert(Observable<List<String>> source) {
-        throw new UnsupportedOperationException("implementation");
+        return source.concatMap(e -> fromIterable(e));
     }
 
     /*
@@ -53,7 +58,7 @@ public Observable<String> convert(Observable<List<String>> source) {
      * return: Observable["a", "b", "c"]
      */
     public Observable<String> distinct(Observable<String> source) {
-        throw new UnsupportedOperationException("implementation");
+        return source.groupBy(e -> e).map(e -> e.getKey());
     }
 
     /*
@@ -61,8 +66,8 @@ public Observable<String> distinct(Observable<String> source) {
      * param: Observable[1, 2, 3, 4, 5] , conditon = x > 2 and x < 5
      * return: Observable[3, 4]
      */
-    public Observable<Integer> filter(Observable<Integer> source, Predicate<Integer> conditon) {
-        throw new UnsupportedOperationException("implementation");
+    public Observable<Integer> filter(Observable<Integer> source, Predicate<Integer> condition) {
+        return source.concatMap(e -> condition.test(e) ? just(e) : empty());
     }
 
     /*
@@ -71,7 +76,7 @@ public Observable<Integer> filter(Observable<Integer> source, Predicate<Integer>
      * return: Maybe[3]
      */
     public Maybe<String> elementAt(Observable<String> source, int index) {
-        throw new UnsupportedOperationException("implementation");
+        return source.zipWith(range(0, MAX_VALUE), (a, b) -> of(a, b)).filter(x -> x.getV2() == index).map(e -> e.getV1()).firstElement();
     }
 
     /*
@@ -80,7 +85,7 @@ public Maybe<String> elementAt(Observable<String> source, int index) {
      * return: Observable["a", "b", "a", "b"]
      */
     public Observable<String> repeat(Observable<String> source, int count) {
-        throw new UnsupportedOperationException("implementation");
+        return range(0, count).concatMap(e -> source);
     }
 
     /*
@@ -89,7 +94,17 @@ public Observable<String> repeat(Observable<String> source, int count) {
      * return: Observable["a", "b"]
      */
     public Observable<String> concat(List<Observable<String>> source) {
-        throw new UnsupportedOperationException("implementation");
+        return create(e -> concat(source, e));
+    }
+    
+    private void concat(List<Observable<String>> source, ObservableEmitter<String> e) {
+        if (source.isEmpty()) {
+            e.onComplete();
+        } else {
+            source.get(0).subscribe(e::onNext, e::onError, () -> {
+                concat(source.subList(1, source.size()), e);
+            });
+        }
     }
 
     /*
@@ -98,7 +113,7 @@ public Observable<String> concat(List<Observable<String>> source) {
      * return: Observable["a", "b"]
      */
     public Observable<String> merge(List<Observable<String>> source) {
-        throw new UnsupportedOperationException("implementation");
+        return fromIterable(source).flatMap(e -> e);
     }
 
     /*
@@ -107,7 +122,7 @@ public Observable<String> merge(List<Observable<String>> source) {
      * return: Observable["a", "b", "c"], 每个元素都延迟1秒
      */
     public Observable<String> delayAll(Observable<String> source, long delay, TimeUnit unit) {
-        throw new UnsupportedOperationException("implementation");
+        return source.concatMap(e -> just(e).delay(delay, unit));
     }
 
 }