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3-sum-closest.cpp
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3-sum-closest.cpp
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// Time: O(n^2)
// Space: O(1)
class Solution {
public:
/**
* @param numbers: Give an array numbers of n integer
* @param target: An integer
* @return: return the sum of the three integers, the sum closest target.
*/
int threeSumClosest(vector<int> nums, int target) {
int ans = INT_MAX;
int min_diff = INT_MAX;
// Make nums in increasing order. Time: O(nlogn)
sort(nums.begin(), nums.end());
for (int i = 0; i < nums.size() - 2; ++i) {
// Skip duplicated.
if (i > 0 && nums[i] == nums[i - 1]) {
continue;
}
int j = i + 1;
int k = nums.size() - 1;
while (j < k) { // Time: O(n) for each i.
const auto sum = nums[i] + nums[j] + nums[k];
if (sum > target) { // Should decrease sum.
--k;
} else if (sum < target) { // Should increase sum.
++j;
} else {
return target;
}
if (abs(sum - target) < min_diff) {
min_diff = abs(sum - target);
ans = sum;
}
}
}
return ans;
}
};