[LeetCode] 16. 3Sum Closest

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.
    For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Thought process:
Sort the array. Iterate through the array. As we iterate, use two pointers: one from start, one from end, to iterate through the array. Use a global variable to keep track of closest sum.

Solution:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
public class Solution {
    public int threeSumClosest(int[] nums, int target) {
        Arrays.sort(nums);
        int closest = target + Integer.MAX_VALUE;
        
        for (int i = 0; i < nums.length; i++) {
            int start = i + 1;
            int end = nums.length - 1;
            
            while (start < end) {
                int threeSum = nums[i] + nums[start] + nums[end];
                int difference = Math.abs(threeSum - target);
          
                if (difference < Math.abs(closest - target)) {
                    closest = threeSum;
                }
                if (threeSum < target) {
                    start++;
                } else {
                    end--;
                }
            }
        }
        
        return closest;
    }
}

Time complexity:
Sorting takes O(nlogn). Loop takes O(n^2). The overall time complexity is O(n^2).
Location: San Jose, CA, USA

Comments

Post a Comment

Popular posts from this blog

[LeetCode] 714. Best Time to Buy and Sell Stock with Transaction Fee

Your are given an array of integers  prices , for which the  i -th element is the price of a given stock on day  i ; and a non-negative integer  fee  representing a transaction fee. You may complete as many transactions as you like, but you need to pay the transaction fee for each transaction. You may not buy more than 1 share of a stock at a time (ie. you must sell the stock share before you buy again.) Return the maximum profit you can make. Example 1: Input: prices = [1, 3, 2, 8, 4, 9], fee = 2 Output: 8 Explanation: The maximum profit can be achieved by: Buying at prices[0] = 1 Selling at prices[3] = 8 Buying at prices[4] = 4 Selling at prices[5] = 9 The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8. Note: 0 < prices.length <= 50000 . 0 < prices[i] < 50000 . 0 <= fee < 50000 . Thought process: Each day there are two options, buy or sell. Use two variables buy and sell to keep track of the max profit. Solutio...
Read more

[LeetCode] 269. Alien Dictionary

There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of  non-empty  words from the dictionary, where  words are sorted lexicographically by the rules of this new language . Derive the order of letters in this language. Example 1: Given the following words in dictionary, [ "wrt", "wrf", "er", "ett", "rftt" ] The correct order is:  "wertf" . Example 2: Given the following words in dictionary, [ "z", "x" ] The correct order is:  "zx" . Example 3: Given the following words in dictionary, [ "z", "x", "z" ] The order is invalid, so return  "" . Note: You may assume all letters are in lowercase. You may assume that if a is a prefix of b, then a must appear before b in the given dictionary. If the order is invalid, return an empty string...
Read more

[LeetCode] 410. Split Array Largest Sum

Given an array which consists of non-negative integers and an integer  m , you can split the array into  m  non-empty continuous subarrays. Write an algorithm to minimize the largest sum among these  m  subarrays. Note: If  n  is the length of array, assume the following constraints are satisfied: 1 ≤  n  ≤ 1000 1 ≤  m  ≤ min(50,  n ) Examples: Input: nums = [7,2,5,10,8] m = 2 Output: 18 Explanation: There are four ways to split nums into two subarrays. The best way is to split it into [7,2,5] and [10,8] , where the largest sum among the two subarrays is only 18. Thought process: Binary search. The range of the answer is between max(nums) and sum(nums). Do a binary search on this range. For every mid value, I check if the array can be split into m sub-arrays, where each sub-array's sum <= mid. If I can, that means mid is too large. Keep the left half. If I can't, that means mid is too small. Keep the...
Read more