add 677

fishercoder1534 · fishercoder1534 · commit cf3d49cecef8 · 2017-09-16T20:48:59.000-07:00
diff --git a/README.md b/README.md
@@ -23,6 +23,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |680|[Valid Palindrome II](https://leetcode.com/problems/valid-palindrome-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_680.java) | O(n) | O(1) | Easy | String
+|677|[Map Sum Pairs](https://leetcode.com/problems/map-sum-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_677.java) | O(n) | O(n) | Medium | HashMap
 |676|[Implement Magic Dictionary](https://leetcode.com/problems/implement-magic-dictionary/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_676.java) | O(n^2) | O(n) | Medium |
 |674|[Longest Continuous Increasing Subsequence](https://leetcode.com/problems/longest-continuous-increasing-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_674.java) | O(n^2) | O(1) | Easy | 
 |672|[Bulb Switcher II](https://leetcode.com/problems/bulb-switcher-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_672.java) | O(1) | O(1) | Medium | Math 
diff --git a/src/test/java/com/fishercoder/_677.java b/src/test/java/com/fishercoder/_677.java
@@ -0,0 +1,55 @@
+package com.fishercoder;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 677. Map Sum Pairs
+ *
+ *  Implement a MapSum class with insert, and sum methods.
+
+ For the method insert, you'll be given a pair of (string, integer).
+ The string represents the key and the integer represents the value.
+ If the key already existed, then the original key-value pair will be overridden to the new one.
+
+ For the method sum, you'll be given a string representing the prefix,
+ and you need to return the sum of all the pairs' value whose key starts with the prefix.
+
+ Example 1:
+
+ Input: insert("apple", 3), Output: Null
+ Input: sum("ap"), Output: 3
+ Input: insert("app", 2), Output: Null
+ Input: sum("ap"), Output: 5
+
+ */
+public class _677 {
+    public static class Solution1 {
+        public static class MapSum {
+
+            Map<String, Integer> map;
+
+            /**
+             * Initialize your data structure here.
+             */
+            public MapSum() {
+                map = new HashMap<>();
+            }
+
+            public void insert(String key, int val) {
+                map.put(key, val);
+            }
+
+            public int sum(String prefix) {
+                int sum = 0;
+                for (String key : map.keySet()) {
+                    if (key.startsWith(prefix)) {
+                        sum += map.get(key);
+                    }
+                }
+                return sum;
+            }
+        }
+
+    }
+}
