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：Two pointers
思路：Two pointers 并 keep comparing and updating closest
Time Complexity: O(N^2) Space Complexity: O(1)
Solution Code：
class Solution {
public int threeSumClosest(int[] nums, int target) {
int min_diff = Integer.MAX_VALUE;
int result = 0;
if(nums == null || nums.length == 0) return result;
Arrays.sort(nums);
for(int i = 0; i < nums.length - 2; i++) {
int target2num = target - nums[i];
// two pointers
int start = i + 1, end = nums.length - 1;
while(start < end) {
int sum2num = nums[start] + nums[end];
int diff = Math.abs(sum2num - target2num);
if(diff < min_diff) {
min_diff = diff;
result = nums[i] + sum2num;
}
if(sum2num <= target2num) {
start++;
}
else {
end--;
}
}
}
return result;
}
}
