3 Sum Closest
出处
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).
Solution
Similar to 3Sum, taking O(n2) time complexity.
固定一个,指针左右动
Complexity
时间复杂度 O(n2 ),空间复杂度 O(1)
Code
public class Solution {
public int threeSumClosest(int[] nums, int target) {
int N = nums.length;
if (N < 3) return 0;
int res = nums[0] + nums[1] + nums[2];
Arrays.sort(nums);
for (int i = 0; i < N-2; ++i)
{
int l = i + 1, r = N - 1;
while (l < r)
{
int threesum = nums[i] + nums[l] + nums[r];
if (threesum == target) return target;
else if (threesum < target) ++l;
else --r;
if (Math.abs(threesum - target) < Math.abs(res - target))
res = threesum;
}
}
return res;
}
}