标签：equal code span get pre integer loop else ica
3Sum
Given a integer array, find all the unique 3-number pairs which sum = 0.
Solution O(N^2):
1. Sort the array, and makes this problem to a equal ‘2sum sorted‘ problem a1 + a2 = -a3(target)
2. from 0 to n-3,
* cc1(if the nums[i] > 0, which means all the numbers following are larger than 0, break to end the loop)
use two pointers from i+1 and n-1,
if nums[lo] + nums[hi] > target, hi--;
if nums[lo] + nums[hi] < target, lo++;
if nums[lo] + nums[hi] == target, init an arraylist and add it into the list<list>
*cc2(skip all the deplicate numbers)
3Sum Cloest (30lines)
Given a integer array and a number target, find the cloest sum of triplet to target.
Similar solution as 3Sum, minimize the Math.abs( a1 + a1 + a3 - target )
Solution O(N^2):
1. Define variables ‘sum‘: the cloest value, ‘compare‘: the minimal difference
2. Sort the array,
when current difference < compare, update sum and compare
there are three if as the problem above to control the ‘lo‘ and ‘hi‘
1 public class Solution { 2 public int threeSumClosest(int[] nums, int target) { 3 Arrays.sort(nums); 4 //length of the array 5 int length = nums.length; 6 //sum of three numbers 7 int sum = target; 8 //difference of target and sum 9 int compare = Integer.MAX_VALUE; 10 //from begin to end, nums[i] is s1 11 for(int i = 0; i < length - 2; i++) { 12 int current = target - nums[i]; 13 //two pointers, nums[lo] is s2, nums[hi] is s3 14 int lo = i + 1, hi = length - 1; 15 while(lo < hi) { 16 //if s1 + s2 - current is smaller than compare, replace it 17 int tmp = Math.abs(nums[lo] + nums[hi] -current); 18 if(tmp < compare) { 19 compare = tmp; 20 sum = nums[lo] + nums[hi] + nums[i]; 21 } 22 //if sum < target, lo++; if sum > target, hi--; if sum == target, end loop 23 if(nums[lo] + nums[hi] + nums[i] < target) lo++; 24 else if(nums[lo] + nums[hi] + nums[i] > target) hi--; 25 else return sum; 26 } 27 } 28 return sum; 29 } 30 }
标签：equal code span get pre integer loop else ica
原文地址：http://www.cnblogs.com/CornerCase/p/6272179.html
