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).
Similar idea to 3Sum, compare each sum with the target, if closer update the current min diff and set the result.
public int threeSumClosest(int[] num, int target) {
if (num==null || num.length<3) {
return -1;
}
//sort array first
Arrays.sort(num);
int result = 0;
int finalDiff = Integer.MAX_VALUE;
for (int i=0; i<num.length-2; i++) {
int start = i+1;
int end = num.length-1;
while (start<end) {
int sum = num[i] + num[start] + num[end];
int diff = Math.abs(sum-target);
if (diff<finalDiff) {
finalDiff = diff;
result = sum;
}
//move start if sum is less than target
if (sum<=target) {
start=start+1;
} else {
end=end-1;
}
}
}
return result;
}