677. Map Sum Pairs

README.md

@@ -118,6 +118,7 @@ continually updating 😃.
 * [307. Range Sum Query - Mutable](src/0307_Range_Sum_Query_Mutable/range_sum_query_mut.go)   *`segment tree`*
 * [404. Sum of Left Leaves](src/0404_sum_of_left_leaves/sum_of_left_leaves.go)   *`binary tree`*
 * [437. Path Sum III](src/0437_path_sum_3/path_sum_3.go)   *`binary tree`*
+* [677. Map Sum Pairs](src/0677_map_sum_pairs/map_sum_pairs.go)   *`trie`*
 * [872. Leaf-Similar Trees](src/0872_leaf_similar_trees/leaf_similar_trees.go)   *`binary tree`*
 
 ### Binary Search

src/0208_implement_trie_prefix_tree/impltrie.go

@@ -36,7 +36,7 @@ func (trie *Trie) Insert(word string) {
 		if _, ok := cur.next[word[i]]; !ok {
 			cur.next[word[i]] = &node{next: make(map[byte]*node)}
 		}
-		cur, _ = cur.next[word[i]]
+		cur = cur.next[word[i]]
 	}
 	if !cur.isWord {
 		cur.isWord = true
@@ -52,9 +52,8 @@ func (trie *Trie) Search(word string) bool {
 		if _, ok := cur.next[word[i]]; !ok {
 			return false
 		}
-		cur, _ = cur.next[word[i]]
+		cur = cur.next[word[i]]
 	}
-
 	return cur.isWord
 }
 
@@ -66,7 +65,7 @@ func (trie *Trie) StartsWith(prefix string) bool {
 		if _, ok := cur.next[prefix[i]]; !ok {
 			return false
 		}
-		cur, _ = cur.next[prefix[i]]
+		cur = cur.next[prefix[i]]
 	}
 	return true
 }

src/0677_map_sum_pairs/map_sum_pairs.go

@@ -0,0 +1,63 @@
+/*
+677. Map Sum Pairs
+https://leetcode.com/problems/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.
+*/
+// time: 2019-02-01
+
+package mapsumpairs
+
+type node struct {
+	val  int
+	next map[rune]*node
+}
+
+// MapSum data structure for solution.
+type MapSum struct {
+	root *node
+}
+
+// Constructor initialize data structure here.
+func Constructor() MapSum {
+	return MapSum{&node{next: make(map[rune]*node)}}
+}
+
+// Insert inserts a word into the trie.
+func (ms *MapSum) Insert(key string, val int) {
+	cur := ms.root
+	for _, c := range key {
+		if _, ok := cur.next[c]; !ok {
+			cur.next[c] = &node{next: make(map[rune]*node)}
+		}
+		cur = cur.next[c]
+	}
+	cur.val = val
+}
+
+// Sum sum of all the pairs' value whose key starts with the prefix.
+func (ms *MapSum) Sum(prefix string) int {
+	cur := ms.root
+	for _, c := range prefix {
+		if _, ok := cur.next[c]; !ok {
+			return 0
+		}
+		cur = cur.next[c]
+	}
+	return sum(cur)
+}
+
+func sum(n *node) int {
+	res := n.val
+	for _, nextNode := range n.next {
+		res += sum(nextNode)
+	}
+	return res
+}

src/0677_map_sum_pairs/map_sum_pairs_test.go

@@ -0,0 +1,20 @@
+package mapsumpairs
+
+import "testing"
+
+func TestMapSumPairs(t *testing.T) {
+	obj := Constructor()
+	obj.Insert("apple", 3)
+	if res := obj.Sum("ap"); res != 3 {
+		t.Errorf("expected %d, got %d", 3, res)
+	}
+
+	obj.Insert("app", 2)
+	if res := obj.Sum("ap"); res != 5 {
+		t.Errorf("expected %d, got %d", 5, res)
+	}
+
+	if res := obj.Sum("al"); res != 0 {
+		t.Errorf("expected %d, got %d", 0, res)
+	}
+}

src/README.md

@@ -101,6 +101,7 @@
 |0455|[Assign Cookies](./0455_assign_cookies/assign_cookies.go)|Easy|*`greedy algorithm`*|
 |0557|[557. Reverse Words in a String III](0557_reverse_words_in_a_string_3/reverse_words_in_a_string_3.go)|Easy|*`string`*|
 |0674|[674. Longest Continuous Increasing Subsequence](0674_longest_continuous_increasing_subsequence/lcis.go)|Easy||
+|0677|[677. Map Sum Pairs](0677_map_sum_pairs/map_sum_pairs.go)|Medium|*`trie`*|
 |0704|[Binary Search](0704_binary_search/binary_search.go)|Easy|*`binary search`*|
 |0713|[713. Subarray Product Less Than K](0713_subarray_product_less_than_k/spltk.go)|Medium|*`sliding window`*|
 |0717|[717. 1-bit and 2-bit Characters](0717_1_bit_and_2_bit_characters/1bitand2bitc.go)|Easy||