Given a sorted linked list, delete all duplicates such that each element appear only once. For example, Given 1->1->2, return 1->2. Given 1->1->2->3->3, return 1->2->3. Thoughts The key of this problem is using the right loop condition. And change what is necessary in each loop. You can use different iteration conditions like the following 2 … Read more
Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ \ 7 … Read more
Given a binary tree, flatten it to a linked list in-place. For example, Given 1 / \ 2 5 / \ \ 3 4 6 The flattened tree should look like: 1 \ 2 \ 3 \ 4 \ 5 \ 6 Java Solution Go down the tree to the left, when the right child … Read more
Given a m * n matrix, if an element is 0, set its entire row and column to 0. Do it in place. Analysis This problem should be solved in place, i.e., no other array should be used. We can use the first column and the first row to track if a row/column should be … Read more
Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node’s key. The right subtree of a node contains only nodes with keys greater than the node’s key. Both the … Read more
Problem: Given a set of non-overlapping & sorted intervals, insert a new interval into the intervals (merge if necessary). Example 1: Given intervals [1,3],[6,9], insert and merge [2,5] in as [1,5],[6,9]. Example 2: Given [1,2],[3,5],[6,7],[8,10],[12,16], insert and merge [4,9] in as [1,2],[3,10],[12,16]. This is because the new interval [4,9] overlaps with [3,5],[6,7],[8,10]. Java Solution 1 … Read more
Problem: Implement pow(x, n). This is a great example to illustrate how to solve a problem during a technical interview. The first and second solution exceeds time limit; the third and fourth are accepted. Java Solution public double myPow(double x, int n){ if(n==0) return 1; if(n<0){ return 1/helper(x, -n); } double v = … Read more
Problem: Implement strStr(). Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. Java Solution 1 – Naive public int strStr(String haystack, String needle) { if(haystack==null || needle==null) return 0; if(needle.length() == 0) return 0; for(int i=0; i<haystack.length(); i++){ if(i + needle.length() > … Read more
Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid. The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not. Analysis A typical problem which can be solved by using a stack data structure. … Read more
Given two sorted integer arrays A and B, merge B into A as one sorted array. Note: You may assume that A has enough space to hold additional elements from B. The number of elements initialized in A and B are m and n respectively. Analysis The key to solve this problem is moving element … Read more
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists. Java Solution The key to solve the problem is defining a fake head. Then compare the first elements from each list. Add the smaller one to the … Read more
Implement atoi to convert a string to an integer. Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases. Analysis The following cases should be considered for this problem: 1. null or empty string 2. white spaces 3. +/- … Read more
Problem: Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Note: Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c) … Read more
Given a collection of intervals, merge all overlapping intervals. For example, Given [1,3],[2,6],[8,10],[15,18], return [1,6],[8,10],[15,18]. Analysis The key to solve this problem is defining a Comparator first to sort the arraylist of Intevals. Java Solution public List<Interval> merge(List<Interval> intervals) { if(intervals == null || intervals.size()<=1){ return intervals; } Collections.sort(intervals, Comparator.comparing((Interval itl)->itl.start)); List<Interval> result … Read more
Implement regular expression matching with support for ‘.’ and ‘*’. ‘.’ Matches any single character. ‘*’ Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). The function prototype should be: bool isMatch(const char *s, const char *p) Some examples: isMatch(“aa”,”a”) return false isMatch(“aa”,”aa”) return true isMatch(“aaa”,”aa”) … Read more