Articles
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149 - Max Points on a Line
Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.
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3 - Longest Substring Without Repeating Characters
Given a string, find the length of the longest substring without repeating characters.
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128 - Longest Consecutive Sequence
Given an unsorted array of integers, find the length of the longest consecutive elements sequence.
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179 - Largest Number
Given a list of non negative integers, arrange them such that they form the largest number.
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378 - Kth Smallest Element in a Sorted Matrix
Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.
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k Sum II
Given n unique integers, number k (1<=k<=n) and target. Find all possible k integers where their sum is target.
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k Sum
Given n distinct positive integers, integer k (k <= n) and a number target. Find k numbers where sum is target. Calculate how many solutions there are?
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208 - Implement Trie
Implement a trie with insert, search, and startsWith methods.
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Interleaving Positive and Negative Numbers
Given an array with positive and negative integers. Re-range it to interleaving with positive and negative integers.
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13 - Roman to Integer
Given a roman numeral, convert it to an integer. The answer is guaranteed to be within the range from 1 to 3999.
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12 - Integer to Roman
Given an integer, convert it to a roman numeral. The number is guaranteed to be within the range from 1 to 3999.
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198 - House Robber
You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacent houses have security system connected and it will automatically contact the police if two adjacent houses were broken into on the same night. Given a list of non-negative integers representing the amount of money of each house, determine the maximum amount of money you can rob tonight without alerting the police.
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134 - Gas Station
There are N gas stations along a circular route, where the amount of gas at station i is gas[i]. You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an empty tank at one of the gas stations. Return the starting gas station’s index if you can travel around the circuit once, otherwise return -1.
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Convert Expression to Polish Notation
Given an expression string array, return the Polish notation of this expression. (remove the parentheses)
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Convert Expression to Reverse Polish Notation
public class Solution { public ArrayList<String> convertToRPN(String[] expression) { ArrayList<String> result = new ArrayList<String>(); if (expression == null || expression.length == 0) return result; Stack<String> stack = new Stack<String>(); for (String s : expression) { if (isOp(s)) { if (s.equals("(")) { stack.push(s); } else if (s.equals(")")) { while (!stack.isEmpty()) { String p = stack.pop(); if (p.equals("(")) { break; } result.add(p); } } else { while (!stack.isEmpty() && order(s) <= order(stack.peek())) {// <= not < 因为如果s与stack.peek()相同order的话，我们要先处理栈里的，因为栈里的operator在表达式左边. 注意区分从左边开始处理和从右边开始处理 此处的<和<= result.add(stack.pop()); } stack.push(s); } } else { result.add(s); } } while (!stack.isEmpty()) { result.add(stack.pop()); } return result; } public boolean isOp(String str) { if (str.equals("+") || str.equals("-") || str.equals("*") || str.equals("/") || str.equals("(") || str.equals(")")) { return true; } else { return false; } } public int order(String str) { if (str.equals("*") || str.equals("/")) { return 2; } else if (str.equals("+") || str.equals("-")) { return 1;//must have } else { return 0; } } } -
150 - Evaluate Reverse Polish Notation
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
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29 - Divide Two Integers
Divide two integers without using multiplication, division and mod operator. If it is overflow, return 2147483647
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Digit Counts
Count the number of k's between 0 and n. k can be 0 - 9.
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Delete Digits
Given string A representative a positive integer which has N digits, remove any k digits of the number, the remaining digits are arranged according to the original order to become a new positive integer. Find the smallest integer after remove k digits.
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248 - Count of Smaller Number
Give you an integer array (index from 0 to n-1, where n is the size of this array, value from 0 to 10000) and an query list. For each query, give you an integer, return the number of element in the array that are smaller that the given integer.
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206 - Interval Sum
Given an integer array (index from 0 to n-1, where n is the size of this array), and an query list. Each query has two integers [start, end]. For each query, calculate the sum number between index start and end in the given array, return the result list.
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205 - Interval Minimum Number
Given an integer array (index from 0 to n-1, where n is the size of this array), and an query list. Each query has two integers [start, end]. For each query, calculate the minimum number between index start and end in the given array, return the result list.
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Segment Tree Modify
For a Maximum Segment Tree, which each node has an extra value max to store the maximum value in this node's interval. Implement a modify function with three parameter root, index and value to change the node's value with [start, end] = [index, index] to the new given value. Make sure after this change, every node in segment tree still has the max attribute with the correct value.
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Segment Tree Query II
For an array, we can build a SegmentTree for it, each node stores an extra attribute count to denote the number of elements in the the array which value is between interval start and end. (The array may not fully filled by elements) Design a query method with three parameters root, start and end, find the number of elements in the in array's interval [start, end] by the given root of value SegmentTree.
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Segment Tree Query
For an integer array (index from 0 to n-1, where n is the size of this array), in the corresponding SegmentTree, each node stores an extra attribute max to denote the maximum number in the interval of the array (index from start to end). Design a query method with three parameters root, start and end, find the maximum number in the interval [start, end] by the given root of segment tree.
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Segmemt Tree Build II
Implement a build method with a given array, so that we can create a corresponding segment tree with every node value represent the corresponding interval max value in the array, return the root of this segment tree.
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Segment Tree Build
The structure of Segment Tree is a binary tree which each node has two attributes start and end denote an segment / interval. start and end are both integers, they should be assigned in following rules:
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11 - Container With Most Water
Given n non-negative integers a1, a2, …, an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find two lines, which together with x-axis forms a container, such that the container contains the most water.
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Coins in a Line II
There are n coins with different value in a line. Two players take turns to take one or two coins from left side until there are no more coins left. The player who take the coins with the most value wins. Could you please decide the first player will win or lose?
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Coins in a Line
There are n coins in a line. Two players take turns to take one or two coins from right side until there are no more coins left. The player who take the last coin wins. Could you please decide the first play will win or lose?
