[crispy] week 4 solution

longest-consecutive-sequence/heozeop.cpp

@@ -0,0 +1,25 @@
+// time complexity: O(n)
+// spatail complexity: O(n)
+
+class Solution {
+public:
+    int longestConsecutive(vector<int>& nums) {
+        unordered_set<int> exisingNum(nums.begin(), nums.end());
+
+        int maxLength = 0, length;
+        for(int num : nums) {
+            if(exisingNum.find(num - 1) != exisingNum.end()) {
+                continue;
+            }
+
+            length = 1;
+            while(exisingNum.find(num + length) != exisingNum.end()) {
+                ++length;
+            }
+
+            maxLength = max(maxLength, length);
+        }
+
+        return maxLength;
+    }
+};

missing-number/heozeop.cpp

@@ -0,0 +1,19 @@
+// time complexity: O(n)
+// spatial complexity: O(n)
+
+class Solution {
+public:
+    int missingNumber(vector<int>& nums) {
+        set<int> exisingNums(nums.begin(), nums.end());
+
+        int answer = -1;
+        for(int i = 0; i <= nums.size(); ++i) {
+            if(exisingNums.find(i) == exisingNums.end()) {
+                answer = i;
+                break;
+            }
+        }
+
+        return answer;
+    }
+};

valid-palindrome/heozeop.cpp

@@ -0,0 +1,23 @@
+// Time Complexity: O(n)
+// Spatial Complexity: O(n)
+
+class Solution {
+public:
+    bool isPalindrome(string s) {
+        string temp = "";
+        for(char c : s) {
+            if(isalnum(c)) {
+                temp += tolower(c);
+            }
+        }
+
+        int length = temp.length();
+        for(int i = 0; i < length / 2; ++i) {
+            if(temp[i] != temp[length - 1 - i]) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+};

word-search/heozeop.cpp

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+// time complexity: O(n * m * 3 ^ L), L은 최대 깊이(문자열 길이)
+// spatial complexity: O((n * m ) ^ 2)
+
+class Solution {
+public:
+  bool exist(vector<vector<char>>& board, string word) {
+    vector<vector<bool>> visit;
+    for(int i = 0; i < board.size(); ++i) {
+      for(int j = 0; j < board[0].size(); ++j) {
+        if(board[i][j] != word[0]) continue;
+        visit = vector(board.size(), vector(board[0].size(), false));
+        visit[i][j] = true;
+        if (find(board, word, 1, {i,j}, visit)) {
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
+
+  bool find(
+    vector<vector<char>>& board, 
+    string word, 
+    int fi, 
+    pair<int,int> curPos, 
+    vector<vector<bool>>& visit
+  ) {
+    if(fi == word.length()) {
+      return true;
+    }
+
+    char target = word[fi];
+    int nr,ny;
+    for(int i = 0; i < 4; ++i) {
+      nr = curPos.first + DIRECTIONS[i][0];
+      ny = curPos.second+ DIRECTIONS[i][1];
+
+      if (isOutSideOfBoard({nr,ny}, {board.size(), board[0].size()}) || visit[nr][ny] || board[nr][ny] != target) {
+        continue;
+      }
+
+      visit[nr][ny] = true;
+      if(find(board, word, fi + 1, {nr,ny}, visit)) {
+        return true;
+      }
+      visit[nr][ny] = false;
+    }
+
+    return false;
+  }
+
+  int DIRECTIONS[4][2] = {
+    {-1, 0},
+    {0, 1},
+    {1, 0},
+    {0, -1},
+  };
+
+  bool isOutSideOfBoard(pair<int,int> cur, pair<int,int> boardSize) {
+    return cur.first < 0 || cur.second < 0 || cur.first >= boardSize.first || cur.second >= boardSize.second;
+  }
+};