[ys-han00] WEEK 01 solutions

contains-duplicate/ys-han00.cpp

@@ -0,0 +1,37 @@
+#include <bits/stdc++.h>
+
+class Solution {
+public:
+    bool containsDuplicate(vector<int>& nums) {
+        sort(nums.begin(), nums.end());
+
+        for(int i = 0; i < nums.size() - 1; i++)
+            if(nums[i] == nums[i+1])
+                return true;
+
+        return false;
+    }
+};
+
+// 첫 시도 및 틀린 풀이
+// 틀린 이유:
+//   leetcode는 처음 풀어보는데, 백준보다 시간 제한이 엄격함
+//   -> 20억 배열 선언하는것만으로도 시간초과 발생
+// 
+// class Solution {
+// public:
+//     bool containsDuplicate(vector<int>& nums) {
+//         vector<bool> check(2'000'000'001, false);
+//         int offset = 1'000'000'000;
+
+//         for(int i = 0; i < nums.size(); i++) {
+//             int idx = nums[i] + offset;
+
+//             if(check[idx] == true)
+//                 return true;
+//             check[idx] = true;
+//         }
+//         return false;
+//     }
+// };
+

house-robber/ys-han00.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        vector<int> dp(nums.size(), 0);
+
+        dp[0] = nums[0];
+        if(dp.size() == 1) 
+            return dp[0];
+
+        dp[1] = nums[1];
+        int ans = max(dp[0], dp[1]);
+
+        for(int i = 2; i < dp.size(); i++) {
+            int maxi = -1;
+            for(int j = 0; j < i - 1; j++)
+                maxi = max(dp[j], maxi);
+            dp[i] = maxi + nums[i];
+            ans = max(ans, dp[i]);
+        }
+
+        return ans;
+    }
+};
+

longest-consecutive-sequence/ys-han00.cpp

@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+
+class Solution {
+public:
+    int longestConsecutive(vector<int>& nums) {
+        if(nums.size() == 0) 
+            return 0;
+
+        sort(nums.begin(), nums.end());
+
+        int ans = 1, cnt = 1;
+        for(int i = 1; i < nums.size(); i++) {
+            if(nums[i] == nums[i - 1])
+                continue;
+            if(nums[i] - 1 == nums[i - 1])
+                cnt++;
+            else
+                cnt = 1;
+            ans = max(cnt, ans);
+        }
+
+        return ans;
+    }
+};
+

top-k-frequent-elements/ys-han00.cpp

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+#include <bits/stdc++.h>
+
+class Solution {
+public:
+    vector<int> topKFrequent(vector<int>& nums, int k) {
+        map<int, int> count;
+
+        for(int i = 0; i < nums.size(); i++) {
+            if(count.find(nums[i]) == count.end())
+                count[nums[i]] = 1;
+            else
+                count[nums[i]]++;
+        }
+
+        vector<pair<int, int>> cnt(count.begin(), count.end());
+        sort(cnt.begin(), cnt.end(), cmp);
+
+        vector<int> ans;
+        for(int i = 0; i < k; i++)
+            ans.push_back(cnt[i].first);
+
+        return ans;
+    }
+
+    static bool cmp(const pair<int, int>& a, const pair<int, int>& b) {
+        return a.second > b.second;
+    }
+};
+

two-sum/ys-han00.cpp

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+#include <bits/stdc++.h>
+
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        vector<pair<int, int>> num_idx;
+        for(int i = 0; i < nums.size(); i++)
+            num_idx.push_back({nums[i], i});
+
+        sort(num_idx.begin(), num_idx.end());
+
+        int left = 0, right = nums.size() - 1;
+        while(1) {
+            if (num_idx[left].first + num_idx[right].first == target)
+                return vector<int>({num_idx[left].second, num_idx[right].second});
+            if(num_idx[left].first + num_idx[right].first < target) left++;
+            else right--;
+        }
+    }
+};
+