LintCode "Subarray Sum Closest"

O(nlgn) - my first thought is, keep maintaining a balanced binary search tree, and then use "Binary Search Tree Closest" one to solve it. But unfortunately there's no on-hand stl class for it. The closest one is multiset<T>.

However, we don't have to use binary search tree. Since we are looking for closest partial sum - we can sort it, then check neighbor 2.

class Solution {
public:
/**
* @param nums: A list of integers
* @return: A list of integers includes the index of the first number
*          and the index of the last number
*/
vector<int> subarraySumClosest(vector<int> nums)
{
if (nums.empty()) {
return {};
}

const int n = nums.size();
vector<pair<int, int>> psum(n + 1);

// Get and Sort the partial sum. a little greedy
for (int i = 0; i < n; ++i) {
psum[i + 1].first = psum[i].first + nums[i];
psum[i + 1].second = i + 1;
}
sort(psum.begin(), psum.end());

int d = INT_MAX;
int ri = 1;
for (int i = 1; i < n + 1; ++i)
{
int curr = abs(psum[i].first - psum[i - 1].first);
if (d > curr)
{
d = curr;
ri = i;
}
}

int l = min(psum[ri - 1].second, psum[ri].second);
int r = -1 + max(psum[ri - 1].second, psum[ri].second);
return {l, r};
}
};