Leetcode--16. 3Sum Closest

题目：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).

思路如下：

对数组排序。

对i从0到length-2：

left = i+1, right = length -1;

当left < right时：

计算sum = array[i] + array[left] + array[right];

计算diff = |target - sum|;

如果diff < mindiff， 更新mindiff，记录closest为sum

如果sum < target，left右移

否则right左移。

返回closest。

C++代码如下：

int threeSumClosest(vector<int>& nums, int target) {
int len = nums.size();
int sum = 0, closest = 0, mindiff = INT_MAX, diff = INT_MAX;
sort(nums.begin(), nums.end());
for (int i = 0; i < len - 2; i++)
{
int left = i + 1, right = len - 1;
while (left < right)
{
sum = nums[i] + nums[left] + nums[right];
diff = abs(sum - target);
if (diff < mindiff)
{
mindiff = diff;
closest = sum;
}
if (sum < target)
left++;
else
right--;
}
}
return closest;
}