[byteho0n] Week 6

container-with-most-water/ekgns33.java

@@ -0,0 +1,83 @@
+/*
+input : array of integer height
+output : maximum amount of water a container can store.
+
+we can build container with two different line (height[i], height[j] when i < j)
+
+example
+1 8 6 2 5 4 8 3 7
+choose i = 1.
+choose j = 4
+   8 ______5 
+    amount of water == (j - i) * min(height[i], height[j])
+   = 3 * 5 = 15
+
+we have to maximize amount of water.
+
+constraints:
+1) is the input array valid?
+length of array is in range [2, 10^5]
+2) positive integers?
+no. range of height is [0, 10 ^4]
+>> check amount can be overflow. 10^4 * 10 ^ 5 = 10^9 < Integer range
+edge:
+1) if length is 2
+return min(height[0], height[1]).
+...
+
+solution 1) brute force;
+iterate through the array from index i = 0 to n-1
+     when n is the length of input array
+    iterate through the array from index j = i + 1 to n;
+        calculate the amount of water and update max amount
+ds : array
+algo : x
+tc : O(n^2) ~= 10^10 TLE
+space : O(1)
+
+solution 2) better 
+ds : array
+algo: two pointer?
+
+two variant for calculating amount of water
+1. height 2. width
+
+set width maximum at first, check heights
+    decrease width one by one
+
+    - at each step width is maximum. 
+        so we have to maximize
+        the minimum between left and right pointer
+
+use left and right pointer 
+while left < right
+
+    calculate amount 
+    compare
+    if height[left] < height[right]
+        move left by one
+    else 
+        vice versa
+
+return max
+tc : O(n)
+sc : O(1)
+
+ */
+class Solution {
+  public int maxArea(int[] height) {
+    int left = 0;
+    int right = height.length - 1;
+    int maxAmount = 0;
+    while(left < right) {
+      int curAmount = (right - left) * Math.min(height[left], height[right]);
+      maxAmount = Math.max(maxAmount, curAmount);
+      if(height[left] < height[right]) {
+        left++;
+      } else {
+        right--;
+      }
+    }
+    return maxAmount;
+  }
+}

design-add-and-search-words-data-structure/ekgns33.java

@@ -0,0 +1,109 @@
+/**
+ design ds that supports add, find
+ find if string matches any previously added string.
+ >> some kind of dictionary
+
+ example
+ add bad
+ add dad
+ add mad
+ search pad >> false
+ search bad >> true
+ search .ad >> true . can be 'b' or 'd' or 'm'
+ search b.. >> true .. can be "ad"
+
+ constraints:
+ 1) empty string can be valid input?
+ nope. lenght of string is in range of [1, 25]
+ 2) string only contiains alphanumeric? or alphabet
+ only lowercase English letters
+ 3) how many queries can be given as input?
+ at most 10^4
+
+ solution 1) brute force
+ save to data structure. for add
+ check every character for all the saved words
+ O(kn) when k is the number of saved words,
+ n is the length of input word token
+ 25 * 25 * 10^4
+ tc : O(kn) + O(kn)
+ add : O(1)
+ search : O(kn)
+ sc : O(kn)
+
+ solution 2) trie?
+
+ save words to trie.
+ when searching
+ do bfs or backtracking dfs
+ if current charcter is . add all childs
+ else add matching childs
+ overall tc : O(sum(m)) + O(n),
+ add : O(m), when m is the length of saved word
+ search : O(n), when n is the length of searh word
+ sc : O(sum(m))
+
+ if volume of search query is much bigger than add query
+ trie solution would be better
+ O(n) search time vs O(mn) search time
+ */
+class WordDictionary {
+  class TrieNode {
+    TrieNode[] childs;
+    boolean isEnd;
+    TrieNode() {
+      childs = new TrieNode[26];
+      isEnd = false;
+    }
+  }
+  TrieNode root;
+  public WordDictionary() {
+    root = new TrieNode();
+  }
+
+  public void addWord(String word) {
+    TrieNode curNode = root;
+    for(char c : word.toCharArray()) {
+      if(curNode.childs[c-'a'] == null) {
+        curNode.childs[c-'a'] = new TrieNode();
+      }
+      curNode = curNode.childs[c-'a'];
+    }
+    curNode.isEnd = true;
+  }
+
+  public boolean search(String word) {
+    return dfsHelper(root, word, 0);
+  }
+
+  public boolean dfsHelper(TrieNode node, String word, int p) {
+    //end clause
+    if(p == word.length()) {
+      return node.isEnd;
+    }
+
+    char curC = word.charAt(p);
+    if(curC == '.') {
+      for(TrieNode next : node.childs) {
+        if(next != null) {
+          if(dfsHelper(next, word, p + 1)) return true;
+        }
+      }
+      return false;
+    } else {
+      if(node.childs[curC-'a'] != null) {
+        if(dfsHelper(node.childs[curC - 'a'], word, p + 1)) return true;
+      }
+      return false;
+    }
+
+
+  }
+}
+
+/**
+ * Your WordDictionary object will be instantiated and called as such:
+ * WordDictionary obj = new WordDictionary();
+ * obj.addWord(word);
+ * boolean param_2 = obj.search(word);
+ */

longest-increasing-subsequence/ekgns33.java

@@ -0,0 +1,60 @@
+/**
+ input : array of integers
+ output : length of the longest strictly increasing subsequence;
+ example
+ 0 1 0 3 2 3 > 0 1 2 3  >> length : 4
+ 4 3 2 1 > 1 >> length : 1
+ 1 1 1 1 > 1 >> length : 1
+
+ constraints :
+ 1) empty array allowed?
+ no, at least one
+
+ solution 1) brute force
+ nested for loop
+ iterate through the array from index i = 0 to n-1 when n is the lenght of input
+ iterate throught the array from index j = i + 1 to n
+ update current Maximum value
+ if bigger than prev max value count ++
+ tc : O(n^2);
+ sc : O(1)
+
+ solution 2) binary search + dp
+ iterate through the array
+ search from saved values.
+ if current value is bigger than everything add
+ else change value
+
+ let val[i] save the smallest value of length i subsequence
+ tc : O(nlogn)
+ sc : O(n)
+
+ */
+
+class Solution {
+  public int lengthOfLIS(int[] nums) {
+    List<Integer> vals = new ArrayList<>();
+    for(int num : nums) {
+      if(vals.isEmpty() || vals.getLast() < num) {
+        vals.add(num);
+      } else {
+        vals.set(binarySearch(vals, num), num);
+      }
+    }
+    return vals.size();
+  }
+  int binarySearch(List<Integer> vals, int num) {
+    int l = 0, r = vals.size()-1;
+    while(l <= r) {
+      int mid = (r - l) / 2+ l;
+      if(vals.get(mid) == num) {
+        return mid;
+      } else if (vals.get(mid) > num) {
+        r = mid - 1;
+      } else {
+        l = mid + 1;
+      }
+    }
+    return l;
+  }
+}

spiral-matrix/ekgns33.java

@@ -0,0 +1,42 @@
+/*
+*.      lr ->
+*   ^   1 2 3 4. rd
+*   lu  5 6 7 8. v
+*        <-  rl
+* tc : O(mn)
+* sc : O(1)
+* */
+
+class Solution {
+  public List<Integer> spiralOrder(int[][] matrix) {
+    int m = matrix.length;
+    int n = matrix[0].length;
+    int lr = 0, rd = 0, rl = n -1, lu = m - 1;
+    int cnt = 0, target = m*n;
+    List<Integer> res = new ArrayList<>();
+
+    while(lr <= rl && rd <= lu) {
+      for(int startLeft = lr; startLeft <= rl; startLeft++) {
+        res.add(matrix[rd][startLeft]);
+      }
+      rd++;
+      for(int startUp = rd; startUp <=lu; startUp++) {
+        res.add(matrix[startUp][rl]);
+      }
+      rl--;
+      if(rd <= lu) {
+        for(int startRight = rl; startRight >= lr; startRight--) {
+          res.add(matrix[lu][startRight]);
+        }
+      }
+      lu--;
+      if(lr <= rl) {
+        for(int startDown = lu; startDown >= rd; startDown--) {
+          res.add(matrix[startDown][lr]);
+        }
+      }
+      lr++;
+    }
+    return res;
+  }
+}

valid-parentheses/ekgns33.java

@@ -0,0 +1,54 @@
+/**
+ input : string s contains just (, ), {, }, [, ]
+ output : return if s is valid
+ valid means that parentheses are matched(balanced)
+ example
+ ((())) : valid
+ (((())) : invalid
+ {() : invalid
+
+ constraint :
+ 1) input string can be empty string?
+ nope. at least one character  >> if length is odd number return false
+ edge:
+ 1) if the length of string is odd number return false
+
+ solution 1)
+ ds : stack
+ algo : x
+ iterate through the string s
+ if opening bracket, add to stack
+ else check the top element of stack
+ if matched pop
+ else return false;
+ return false
+
+ tc : O(n)
+ sc : O(n) worst case : every character is opening bracket
+
+ */
+class Solution {
+  public boolean isValid(String s) {
+    //edge
+    if(s.length() % 2 == 1) return false;
+    // we can use deque instead
+    Stack<Character> stack = new Stack<>();
+
+    for(char c : s.toCharArray()) {
+      if(c == '(' || c == '{' || c == '[') {
+        stack.push(c);
+      } else {
+        if(stack.isEmpty()) return false;
+        if(c == ')') {
+          if(stack.peek() != '(') return false;
+        } else if (c == '}') {
+          if(stack.peek() != '{') return false;
+        } else if (c == ']'){
+          if(stack.peek() != '[') return false;
+        }
+        stack.pop();
+      }
+    }
+    return stack.isEmpty();
+  }
+}