[CareerCup] 17.8 Contiguous Sequence with Largest Sum 連續子序列之和最大

 

17.8 You are given an array of integers (both positive and negative). Find the contiguous sequence with the largest sum. Return the sum.

 

LeetCode上的原題，請參見我之前的部落格Maximum Subarray。

 

解法一：

int get_max_sum(vector<int> nums) {
    int res = INT_MIN, sum = INT_MIN;
    for (auto a : nums) {
        sum = max(sum + a, a);
        res = max(res, sum);
    }
    return res;
}

 

解法二：

int helper(vector<int> nums, int left, int right) {
    if (left >= right) return nums[left];
    int mid = left + (right - left) / 2;
    int lmax = helper(nums, left, mid - 1);
    int rmax = helper(nums, mid + 1, right);
    int mmax = nums[mid], t = nums[mid];
    for (int i = mid - 1; i >= left; --i) {
        t += nums[i];
        mmax = max(mmax, t);
    }
    t = mmax;
    for (int i = mid + 1; i <= right; ++i) {
        t += nums[i];
        mmax = max(mmax, t);
    }
    return max(mmax, max(lmax, rmax));
}

int get_max_sum(vector<int> nums) {
    return helper(nums, 0, nums.size() - 1);
}

 

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