leetcode 中等(设计)：[146, 155, 208, 211, 284, 304, 307, 341, 355, 380]
目录
146. LRU 缓存
var LRUCache = function (capacity) {
this.capacity = capacity;
this.map = new Map();
};
LRUCache.prototype.get = function (key) {
if (this.map.has(key)) {
let value = this.map.get(key);
this.map.delete(key);
this.map.set(key, value);
return value;
}
return -1;
};
LRUCache.prototype.put = function (key, value) {
this.map.delete(key);
this.map.set(key, value);
if (this.map.size > this.capacity) {
this.map.delete(this.map.keys().next().value);
}
};
155. 最小栈
var MinStack = function () {
this.data = [];
};
MinStack.prototype.push = function (val) {
this.data.push(val);
};
MinStack.prototype.pop = function () {
this.data.pop();
};
MinStack.prototype.top = function () {
return this.data[this.data.length - 1];
};
MinStack.prototype.getMin = function () {
return Math.min(...this.data);
};
208. 实现 Trie (前缀树)
var Trie = function () {
this.data = {};
};
Trie.prototype.insert = function (word) {
this.data[word] = word;
};
Trie.prototype.search = function (word) {
return !!this.data[word];
};
Trie.prototype.startsWith = function (prefix) {
for (const key in this.data) {
if (this.data[key].startsWith(prefix)) {
return true;
}
}
return false;
};
211. 添加与搜索单词 - 数据结构设计
var WordDictionary = function () {
this.data = {};
};
WordDictionary.prototype.addWord = function (word) {
if (!this.data[word.length]) {
// 键为单词长度，值为同长度的单词集合
this.data[word.length] = [];
}
this.data[word.length].push(word);
};
WordDictionary.prototype.search = function (word) {
const len = word.length;
if (!this.data[len]) return false;
if (!word.includes(".")) return this.data[len].includes(word); // 普通字符串，直接从等长单词集合中查找即可
// 否则是正则表达式，先创建正则表达式对象
const reg = new RegExp(word);
return this.data[len].some((item) => reg.test(item));
};
284. 顶端迭代器
var PeekingIterator = function (iterator) {
this.data = [];
while (iterator.hasNext()) this.data.push(iterator.next());
this.index = 0;
this.size = this.data.length;
};
PeekingIterator.prototype.peek = function () {
return this.data[this.index];
};
PeekingIterator.prototype.next = function () {
return this.data[this.index++];
};
PeekingIterator.prototype.hasNext = function () {
return this.index < this.size;
};
304. 二维区域和检索 - 矩阵不可变
var NumMatrix = function (matrix) {
this.data = matrix;
};
NumMatrix.prototype.sumRegion = function (row1, col1, row2, col2) {
let sum = 0;
for (let i = row1; i <= row2; i++) {
for (let j = col1; j <= col2; j++) {
sum += this.data[i][j];
}
}
return sum;
};
307. 区域和检索 - 数组可修改
var NumArray = function (nums) {
this.data = nums;
};
NumArray.prototype.update = function (index, val) {
this.data[index] = val;
};
NumArray.prototype.sumRange = function (left, right) {
let sum = 0;
for (let i = left; i <= right; i++) {
sum += this.data[i];
}
return sum;
};
341. 扁平化嵌套列表迭代器
// 方法一：
var NestedIterator = function (nestedList) {
this.list = [];
this.traverse(nestedList);
};
NestedIterator.prototype.traverse = function (arr) {
for (let i = 0; i < arr.length; i++) {
if (arr[i].isInteger()) {
this.list.push(arr[i].getInteger()); // 是Integer
} else {
this.traverse(arr[i].getList()); // 是List，递归调用
}
}
};
NestedIterator.prototype.hasNext = function () {
return this.list.length > 0;
};
NestedIterator.prototype.next = function () {
return this.list.shift();
};
// 方法二：
var NestedIterator_1 = function (nestedList) {
this.list = nestedList
.toString()
.split(",")
.filter((val) => {
return val != "";
});
};
NestedIterator_1.prototype.toString = function () {
if (this.isInteger()) {
return this.getInteger() + "";
} else {
return this.getList().toString();
}
};
NestedIterator_1.prototype.hasNext = function () {
return this.list.length > 0;
};
NestedIterator_1.prototype.next = function () {
return this.list.shift();
};
355. 设计推特
var Twitter = function () {
this.tweets = {};
this.user = {};
this.time = 0;
};
Twitter.prototype.postTweet = function (userId, tweetId) {
if (!this.tweets[userId]) {
this.tweets[userId] = [];
}
this.tweets[userId].push({ tweetId, twitTime: this.time++ });
};
Twitter.prototype.getNewsFeed = function (userId) {
let followsId = Array.from(this.user[userId] || {});
followsId.push(userId);
const allTwitters = followsId
.reduce((prev, next) => prev.concat(this.tweets[next] || []), [])
.sort((a, b) => b.twitTime - a.twitTime)
.map((item) => item.tweetId);
return Array.from(new Set(allTwitters)).slice(0, 10);
};
Twitter.prototype.follow = function (followerId, followeeId) {
if (!this.user[followerId]) {
this.user[followerId] = new Set();
}
this.user[followerId].add(followeeId);
};
Twitter.prototype.unfollow = function (followerId, followeeId) {
if (this.user[followerId]) {
this.user[followerId].delete(followeeId);
}
};
380. O(1) 时间插入、删除和获取随机元素
var RandomizedSet = function () {
this.data = new Set();
};
RandomizedSet.prototype.insert = function (val) {
if (this.data.has(val)) {
return false;
} else {
this.data.add(val);
return true;
}
};
RandomizedSet.prototype.remove = function (val) {
return this.data.delete(val);
};
RandomizedSet.prototype.getRandom = function () {
let random = Math.floor(Math.random() * this.data.size);
return Array.from(this.data)[random];
};
