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Commit 8cdc0a3

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添加部分哈希表题目
1 parent dde4f6f commit 8cdc0a3

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/*
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* @lc app=leetcode.cn id=786 lang=cpp
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*
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* [786] 第 K 个最小的素数分数
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*/
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// @lc code=start
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class Solution {
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public:
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// vector<int> kthSmallestPrimeFraction(vector<int>& arr, int k) {
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// int n = arr.size();
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// vector<vector<int>> vec;
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// for (int i = 0; i < n; i++) {
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// for (int j = i + 1; j < n; j++) {
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// vec.push_back({ arr[i], arr[j] });
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// }
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// }
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// sort(vec.begin(), vec.end(), [](const vector<int>& a, const vector<int>& b) -> bool {
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// return a[0] * b[1] < b[0] * a[1];
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// });
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// return vec[k-1];
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// }
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vector<int> kthSmallestPrimeFraction(vector<int>& arr, int k) {
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int n = arr.size();
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double left = 0.0;
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double right = 1.0;
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while (left < right) {
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double mid = left + (right - left) / 2;
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vector<int> ans = { 0, 1 };
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// mid 左边有多少个
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int count = left_count(arr, mid, ans);
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if (count == k) // mid 左边正好有 k 个,即为ans
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return ans;
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else if (count < k)
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left = mid;
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else
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right = mid;
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}
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return { 0, 1 };
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}
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int left_count(const vector<int>& arr, double mid, vector<int>& bound) {
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int count = 0;
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// 两层for循环仍可以优化
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for (int j = 1; j < arr.size(); j++) {
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for (int i = 0; i < j; i++) {
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if ((double) arr[i] / arr[j] < mid) {
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count++;
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if (arr[i] * bound[1] > bound[0] * arr[j]) {
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bound[0] = arr[i];
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bound[1] = arr[j];
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}
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} else {
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break;
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}
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}
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}
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return count;
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}
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};
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// @lc code=end
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‎二分查找/910.最小差值-ii.cpp‎

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/*
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* @lc app=leetcode.cn id=910 lang=cpp
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*
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* [910] 最小差值 II
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*/
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// @lc code=start
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class Solution {
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public:
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int smallestRangeII(vector<int>& nums, int k) {
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sort(nums.begin(), nums.end());
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int n = nums.size();
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int E = nums[n-1] - nums[0];
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// 从1到nums.size()的长度中任意一点都有可能是中间点
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for (int i = 1; i < n; i++) {
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int min_val = min(nums[0] + k, nums[i] - k);
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int max_val = max(nums[n-1] - k, nums[i-1] + k);
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E = min(E, max_val-min_val);
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}
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return E;
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}
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};
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// @lc code=end
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‎二分查找/912.排序数组.cpp‎

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/*
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* @lc app=leetcode.cn id=912 lang=cpp
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*
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* [912] 排序数组
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*/
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// @lc code=start
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class Solution {
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public:
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vector<int> sortArray(vector<int>& nums) {
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sort(nums.begin(), nums.end());
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return nums;
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}
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};
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// @lc code=end
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‎哈希表/187.重复的dna序列.cpp‎

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/*
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* @lc app=leetcode.cn id=187 lang=cpp
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*
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* [187] 重复的DNA序列
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*/
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// @lc code=start
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class Solution {
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public:
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vector<string> findRepeatedDnaSequences(string s) {
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if (s.size() <= 10) return { };
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unordered_set<string> memo;
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unordered_set<string> res;
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vector<string> ans;
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for (int i = 0; i < s.size() - 9; i++) {
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string a = s.substr(i, 10);
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if (memo.find(a) != memo.end()) {
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res.insert(a);
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}
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memo.insert(a);
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}
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for (auto& item : res) {
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ans.push_back(item);
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}
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return ans;
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}
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};
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// @lc code=end
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‎哈希表/204.计数质数.cpp‎

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/*
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* @lc app=leetcode.cn id=204 lang=cpp
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*
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* [204] 计数质数
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*/
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// @lc code=start
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class Solution {
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public:
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int countPrimes(int n) {
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vector<bool> isPrime(n, true);
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int ans = 0;
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for (int i = 2; i < n; i++)
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{
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if (isPrime[i]) {
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ans++;
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// i 的倍数都不是质数
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int m = 2;
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while (m * i < n)
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{
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isPrime[m*i] = false;
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m++;
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}
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}
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}
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return ans;
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}
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};
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// @lc code=end
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‎哈希表/205.同构字符串.cpp‎

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/*
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* @lc app=leetcode.cn id=205 lang=cpp
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*
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* [205] 同构字符串
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*/
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// @lc code=start
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class Solution {
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public:
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bool isIsomorphic(string s, string t) {
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if (s.size() != t.size()) return false;
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int n = s.size();
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unordered_map<char, char> map;
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unordered_set<char> memo;
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for (int i = 0; i < n; i++) {
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if (map.find(s[i]) == map.end()) {
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// 已经被映射过了
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if (memo.find(t[i]) != memo.end())
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return false;
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map[s[i]] = t[i];
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memo.insert(t[i]);
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} else {
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if (map[s[i]] != t[i])
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return false;
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}
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}
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return true;
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}
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};
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// @lc code=end
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‎哈希表/217.存在重复元素.cpp‎

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/*
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* @lc app=leetcode.cn id=217 lang=cpp
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*
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* [217] 存在重复元素
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*/
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// @lc code=start
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class Solution {
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public:
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bool containsDuplicate(vector<int>& nums) {
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unordered_set<int> st;
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for (int a : nums) {
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if (st.find(a) != st.end())
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return true;
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st.insert(a);
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}
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return false;
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}
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};
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// @lc code=end
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/*
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* @lc app=leetcode.cn id=219 lang=cpp
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*
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* [219] 存在重复元素 II
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*/
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// @lc code=start
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class Solution {
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public:
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bool containsNearbyDuplicate(vector<int>& nums, int k) {
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unordered_map<int, int> map;
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for (int i = 0; i < nums.size(); i++) {
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if (map.find(nums[i]) != map.end() && abs(i - map[nums[i]]) <= k)
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return true;
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map[nums[i]] = i;
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}
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return false;
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}
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};
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// @lc code=end
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‎哈希表/274.h-指数.cpp‎

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/*
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* @lc app=leetcode.cn id=274 lang=cpp
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*
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* [274] H 指数
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*/
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// @lc code=start
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class Solution {
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public:
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int hIndex(vector<int>& citations) {
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sort(citations.begin(), citations.end());
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int m = citations.size();
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int left = 0;
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int right = m - 1;
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while (left < right)
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{
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int mid = left + (right - left) / 2;
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if (citations[mid] >= (m - mid)) {
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right = mid;
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} else {
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left = mid + 1;
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}
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}
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if (citations[right] == 0) return 0; // testcase: [0]
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return m - right;
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}
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};
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// @lc code=end
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‎哈希表/290.单词规律.cpp‎

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/*
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* @lc app=leetcode.cn id=290 lang=cpp
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*
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* [290] 单词规律
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*/
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// @lc code=start
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class Solution {
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public:
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bool wordPattern(string pattern, string s) {
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unordered_map<char, string> map;
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unordered_set<string> hasMap;
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vector<string> words;
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split(s, words);
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if (pattern.size() != words.size())
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return false;
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for (int i = 0; i < pattern.size(); i++) {
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char c = pattern[i];
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if (map.find(c) == map.end()) {
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// a 和 b 不能同时映射到同一个单词
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if (hasMap.find(words[i]) != hasMap.end()) {
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return false;
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}
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// cout << "c="<< c << "; wordds[i]=" << words[i] << endl;
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map[c] = words[i];
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hasMap.insert(words[i]);
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} else {
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if (map[c] != words[i]) {
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// cout << "c="<< c << "; wordds[i]=" << words[i] << endl;
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return false;
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}
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}
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}
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return true;
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}
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void split(const string& s, vector<string>& words) {
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string str = "";
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for (char c : s) {
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if (c == ' ') {
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words.push_back(str);
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str = "";
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} else {
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str += c;
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}
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}
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if (str != "") {
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words.push_back(str);
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}
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}
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};
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// @lc code=end
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