剑指 Offer II 066. 单词之和
实现一个 MapSum 类，支持两个方法，insert 和 sum：
MapSum() 初始化 MapSum 对象void insert(String key, int val) 插入 key-val 键值对，字符串表示键 key ，整数表示值 val 。如果键 key 已经存在，那么原来的键值对将被替代成新的键值对。int sum(string prefix) 返回所有以该前缀 prefix 开头的键 key 的值的总和。
示例：
输入：
inputs = ["MapSum", "insert", "sum", "insert", "sum"]
inputs = [[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
输出：
[null, null, 3, null, 5]
解释：
MapSum mapSum = new MapSum();
mapSum.insert("apple", 3);
mapSum.sum("ap"); // return 3 (apple = 3)
mapSum.insert("app", 2);
mapSum.sum("ap"); // return 5 (apple + app = 3 + 2 = 5)
提示：
1 <= key.length, prefix.length <= 50key 和 prefix 仅由小写英文字母组成1 <= val <= 100050 次 insert 和 sum
注意：本题与主站 677 题相同： https://leetcode.cn/problems/map-sum-pairs/
原站题解
python3 解法, 执行用时: 40 ms, 内存消耗: 15.1 MB, 提交时间: 2022-11-17 16:30:16
class MapSum:
def __init__(self):
self.map = {}
self.prefixmap = {}
def insert(self, key: str, val: int) -> None:
delta = val
if key in self.map:
delta -= self.map[key]
self.map[key] = val
for i in range(len(key)):
currprefix = key[0:i+1]
if currprefix in self.prefixmap:
self.prefixmap[currprefix] += delta
else:
self.prefixmap[currprefix] = delta
def sum(self, prefix: str) -> int:
if prefix in self.prefixmap:
return self.prefixmap[prefix]
else:
return 0
# Your MapSum object will be instantiated and called as such:
# obj = MapSum()
# obj.insert(key,val)
# param_2 = obj.sum(prefix)
golang 解法, 执行用时: 0 ms, 内存消耗: 2.6 MB, 提交时间: 2022-11-17 16:29:51
// 前缀哈希映射
type MapSum struct {
m, pre map[string]int
}
func Constructor() MapSum {
return MapSum{map[string]int{}, map[string]int{}}
}
func (m *MapSum) Insert(key string, val int) {
delta := val
if m.m[key] > 0 {
delta -= m.m[key]
}
m.m[key] = val
for i := range key {
m.pre[key[:i+1]] += delta
}
}
func (m *MapSum) Sum(prefix string) int {
return m.pre[prefix]
}
/**
* Your MapSum object will be instantiated and called as such:
* obj := Constructor();
* obj.Insert(key,val);
* param_2 := obj.Sum(prefix);
*/
golang 解法, 执行用时: 4 ms, 内存消耗: 2.4 MB, 提交时间: 2022-11-17 16:29:06
type MapSum map[string]int
func Constructor() MapSum {
return MapSum{}
}
func (m MapSum) Insert(key string, val int) {
m[key] = val
}
func (m MapSum) Sum(prefix string) (sum int) {
for s, v := range m {
if strings.HasPrefix(s, prefix) {
sum += v
}
}
return
}
/**
* Your MapSum object will be instantiated and called as such:
* obj := Constructor();
* obj.Insert(key,val);
* param_2 := obj.Sum(prefix);
*/
python3 解法, 执行用时: 40 ms, 内存消耗: 15.1 MB, 提交时间: 2022-11-17 16:28:48
'''
暴力扫描
'''
class MapSum:
def __init__(self):
self.map = {}
def insert(self, key: str, val: int) -> None:
self.map[key] = val
def sum(self, prefix: str) -> int:
res = 0
for key,val in self.map.items():
if key.startswith(prefix):
res += val
return res
# Your MapSum object will be instantiated and called as such:
# obj = MapSum()
# obj.insert(key,val)
# param_2 = obj.sum(prefix)