add and modifed some solutions

Author: chihungyu1116

127 Word Ladder.js

@@ -65,4 +65,77 @@ var ladderLength = function(beginWord, endWord, wordList) {
     }
 
     return 0;
-};
+};
+
+// will time exceeded. javascript hash is slower than set
+var ladderLength = function(beginWord, endWord, wordList) {
+    if(beginWord === endWord) {
+        return 0;
+    }
+    
+    var queue = [];
+    var visited = {};
+    var count = 1;
+    var baseCharCode = 'a'.charCodeAt(0);
+    
+    queue.push(beginWord);
+    
+    while(queue.length) {
+        var len = queue.length;
+        
+        for(var i = 0; i < len; i++) {
+            var word = queue.shift();
+            
+            for(var j = 0; j < word.length; j++) {
+                for(var k = 0; k < 26; k++) {
+                    var newChar = String.fromCharCode(baseCharCode + k);
+                    var newWord = word.substring(0, j) + newChar + word.substring(j + 1);
+                    
+                    if(newWord === endWord) {
+                        return count + 1;
+                    }
+                    
+                    if(!visited[newWord] && wordList.has(newWord)) {
+                        visited[newWord] = true;
+                        queue.push(newWord);
+                    }
+                }
+            }    
+        }
+        
+        count++;
+    }
+    
+    return 0;
+};
+
+
+
+
+Hi Thiago
+
+I very much appreciate that you took the time writing this warm welcoming letter and provided me the opportunity to come onsite visiting the team at Periscope.
+After much thought, I've decided to accept offer at another company. It was really a tough call for me since I really like the product, role and people I met during my visit. 
+Again, I cannot thank you enough for your time, and support. It's been a great pleasure to know you and the team. I hope that we cross paths in the near future.
+
+Wish you, teams, and Periscope all the success.
+
+Regards,
+Jerry
+
+
+
+
+Hi Cynthia
+
+Thank your for patience and support along the way.
+I very much appreciate that you took the time answering many of my questions about the Periscope, and role.
+
+After much thought, I've decided to accept offer at another company. It was really a tough call for me since I really like the product and people I met during my visit.
+ 
+Again, I cannot thank you enough for your time, and support. It's been a great pleasure to know you and the team. I hope that we cross paths in the near future.
+
+Wish you, teams, and Periscope all the success.
+
+Regards,
+Jerry

128 Longest Consecutive Sequence.js

@@ -0,0 +1,52 @@
+// Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
+
+// For example,
+// Given [100, 4, 200, 1, 3, 2],
+// The longest consecutive elements sequence is [1, 2, 3, 4]. Return its length: 4.
+
+// Your algorithm should run in O(n) complexity.
+
+// Hide Company Tags Google Facebook
+// Hide Tags Array Union Find
+// Hide Similar Problems (M) Binary Tree Longest Consecutive Sequence
+
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var longestConsecutive = function(nums) {
+    var maxLen = -Infinity;
+    var hash = {};
+    
+    for(var i = 0; i < nums.length; i++) {
+        hash[nums[i]] = 1;
+    }
+    
+    var visited = {};
+    
+    for(i = 0; i < nums.length; i++) {
+        var val = nums[i];
+        if(visited[val]) {
+            continue;
+        }
+        visited[val] = true;
+        var len = 1;
+        var preVal = val - 1;
+        while(hash[preVal]) {
+            len++
+            visited[preVal--] = true;
+        }
+        var nxtVal = val + 1;
+        while(hash[nxtVal]) {
+            len++
+            visited[nxtVal++] = true;
+        }
+        
+        if(len > maxLen) {
+            maxLen = len;
+        }
+    }
+    
+    return maxLen;
+};

146 LRU Cache.js

@@ -91,4 +91,116 @@ LRUCache.prototype.set = function(key, value) {
     }
 
     this.map.set(key, newNode);
-};
+};
+
+
+
+
+
+
+
+
+
+
+// Second Implementation
+
+
+function DoublyLinkListNode(key, value) {
+    this.key = key;
+    this.value = value;
+    this.prev = this.next = null;
+}
+
+/**
+ * @constructor
+ */
+var LRUCache = function(capacity) {
+    this.head = this.tail = null;
+    this.maxCapacity = capacity;
+    this.currSize = 0;
+    this.hash = {};
+};
+
+/**
+ * @param {number} key
+ * @returns {number}
+ */
+LRUCache.prototype.get = function(key) {
+    if(!this.hash[key]) {
+        return -1;
+    }
+    
+    this.moveToHead(key);
+    return this.hash[key].value;
+};
+
+/**
+ * @param {number} key
+ * @param {number} value
+ * @returns {void}
+ */
+LRUCache.prototype.set = function(key, value) {
+    if(this.maxCapacity <= 0) {
+        return;
+    }
+
+    if(!this.hash[key]) {
+
+        if(this.currSize === this.maxCapacity) {
+            this.removeLast();
+            this.currSize--;
+        }
+        
+        this.hash[key] = new DoublyLinkListNode(key, value);
+        this.currSize++;
+    }
+    
+    this.hash[key].value = value;
+    this.moveToHead(key);
+};
+
+LRUCache.prototype.removeLast = function() { 
+    if(this.tail === null) {
+        return;
+    }
+
+    delete this.hash[this.tail.key];
+    var newTail = this.tail.prev;
+
+    if(newTail === null) {
+        this.head = this.tail = null;
+        return;
+    }
+
+    this.tail.prev = null;
+    newTail.next = null;
+    this.tail = newTail;
+}
+
+LRUCache.prototype.moveToHead = function(key) {
+    var newHead = this.hash[key];
+    
+    if(this.head === null && this.tail === null) {
+        this.head = this.tail = newHead;
+    }
+
+    if(newHead === this.head) {
+        return;
+    }
+    
+    if(newHead === this.tail) {
+        this.tail = newHead.prev;
+    }
+    
+    if(newHead.prev) {
+        newHead.prev.next = newHead.next;    
+    }
+    if(newHead.next) {
+        newHead.next.prev = newHead.prev;    
+    }
+    
+    newHead.prev = null;
+    newHead.next = this.head;
+    this.head.prev = newHead;
+    this.head = newHead;
+}

157 Read N Characters Given Read4.js

@@ -54,4 +54,7 @@ var solution = function(read4) {
 
         return total;
     };
-};
+};
+
+
+// [tricky] [important]

158 Read N Characters Give Read4 II - Call Multiple Times.js

@@ -0,0 +1,65 @@
+// The API: int read4(char *buf) reads 4 characters at a time from a file.
+
+// The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.
+
+// By using the read4 API, implement the function int read(char *buf, int n) that reads n characters from the file.
+
+// Note:
+// The read function may be called multiple times.
+
+// Hide Company Tags Bloomberg Google Facebook
+// Hide Tags String
+// Hide Similar Problems (E) Read N Characters Given Read4
+
+
+
+/**
+ * Definition for read4()
+ * 
+ * @param {character[]} buf Destination buffer
+ * @return {number} The number of characters read
+ * read4 = function(buf) {
+ *     ...
+ * };
+ */
+
+/**
+ * @param {function} read4()
+ * @return {function}
+ */
+var solution = function(read4) {
+    let bufRead = [];
+    let count = 0; // how many characters read with read4
+    let i = 0;
+        
+    /**
+     * @param {character[]} buf Destination buffer
+     * @param {number} n Maximum number of characters to read
+     * @return {number} The number of characters read
+     */
+    return function(buf, n) {
+        let numChrRead = 0;
+        
+        while (numChrRead < n) {
+            if (i === 0) {
+                count = read4(bufRead);
+            }
+            
+            while (i < count && numChrRead < n) {
+                buf[numChrRead++] = bufRead[i++];
+            }
+            
+            // read4 buffer used up, start over
+            if (i === count) {
+                i = 0;
+            }
+            
+            // end of file
+            if (count < 4) {
+                break;
+            }
+        }
+        
+        return numChrRead;
+    };
+};

20 Valid Parentheses.js

@@ -27,5 +27,26 @@ var isValid = function(s) {
         index++;
     }
 
+    return stack.length === 0;
+};
+
+// second attempt
+
+var isValid = function(s) {
+    var stack = [];
+    
+    for(var i = 0; i < s.length; i++) {
+        var chr = s[i];
+        
+        if(chr === '(' || chr === '{' || chr === '[') {
+            stack.push(chr);
+        } else if(chr === ')' || chr === '}' || chr === ']') {
+            var top = stack.pop();
+            if(!top || (top === '(' && chr !== ')') || (top === '{' && chr !== '}') || (top === '[' && chr !== ']')) {
+                return false;
+            }
+        }
+    }
+    
     return stack.length === 0;
 };