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fix format, and a little problem caused by #8 #9

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fix format, and a little problem caused by #8 #9

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4 changes: 2 additions & 2 deletions 014. Maximum Subarray/main.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -7,8 +7,8 @@ int main()
Solution s;
std::cout << s.maxSubArray(A, 9) << std::endl;

SolutionByDivideAndConquer dac;
std::cout << s.maxSubArray(A, 9) << std::endl;
SolutionByDivideAndConquer dac;
std::cout << dac.maxSubArray(A, 9) << std::endl;

return 0;
}
72 changes: 36 additions & 36 deletions 014. Maximum Subarray/solution.h
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Expand Up @@ -14,42 +14,42 @@ class Solution {
};

class SolutionByDivideAndConquer{
//O(n)
int find_max_crossing_subarray(int arr[], unsigned low, unsigned mid, unsigned hgh)
{
auto accumulation = 0;

auto lft_sum = accumulation = arr[mid];
if (mid > low)
for (auto i = mid - 1; i != low - 1; --i)
if ((accumulation += arr[i]) > lft_sum)
lft_sum = accumulation;

auto rht_sum = accumulation = arr[mid + 1];
if (hgh > mid)
for (auto i = mid + 2; i != hgh + 1; ++i)
if ((accumulation += arr[i]) > rht_sum)
rht_sum = accumulation;

return lft_sum + rht_sum;
}

//O(n lg n)
int divide_and_conquer(int arr[], unsigned low, unsigned hgh)
{
if (low == hgh) return arr[low];

auto mid = (low + hgh) / 2;
auto lft = divide_and_conquer(arr, low, mid);
auto rht = divide_and_conquer(arr, mid + 1, hgh);
auto crs = find_max_crossing_subarray(arr, low, mid, hgh);

return std::max({ lft, rht, crs });
}
//O(n)
int find_max_crossing_subarray(int arr[], unsigned low, unsigned mid, unsigned hgh)
{
auto accumulation = 0;

auto lft_sum = accumulation = arr[mid];
if (mid > low)
for (auto i = mid - 1; i != low - 1; --i)
if ((accumulation += arr[i]) > lft_sum)
lft_sum = accumulation;

auto rht_sum = accumulation = arr[mid + 1];
if (hgh > mid)
for (auto i = mid + 2; i != hgh + 1; ++i)
if ((accumulation += arr[i]) > rht_sum)
rht_sum = accumulation;

return lft_sum + rht_sum;
}

//O(n lg n)
int divide_and_conquer(int arr[], unsigned low, unsigned hgh)
{
if (low == hgh) return arr[low];

auto mid = (low + hgh) / 2;
auto lft = divide_and_conquer(arr, low, mid);
auto rht = divide_and_conquer(arr, mid + 1, hgh);
auto crs = find_max_crossing_subarray(arr, low, mid, hgh);

return std::max({ lft, rht, crs });
}

public:
int maxSubArray(int A[], int n)
{
return divide_and_conquer(A, 0, n - 1);
}
int maxSubArray(int A[], int n)
{
return divide_and_conquer(A, 0, n - 1);
}
};