Find maximum Subsequence Sum according to given conditions
Given an integer array nums and an integer K, The task is to find the maximum sum of a non-empty subsequence of the array such that for every two consecutive integers in the subsequence, nums[i] and nums[j], where i < j, the condition j – i <= K is satisfied.
A subsequence of an array is obtained by deleting some number of elements (can be zero) from the array, leaving the remaining elements in their original order.
Input: nums = [10, 2, -10, 5, 20], K = 2 Output: 37 Explanation: The subsequence is [10, 2, 5, 20]. Input: nums = [-1, -2, -3], K = 1 Output: -1 Input: nums = [10, -2, -10, -5, 20], K = 2 Output: 23
- The optimal solution of this problem can be achieved by using the Sliding Window Maximum and Dynamic Programming .
- At any index i after calculating the maximum sum for i, nums[i] will now store the maximum possible sum that can be obtained from a subsequence ending at i.
- To calculate the maximum possible sum for every index i , check what is the maximum value that can be obtained from a window of size K before it. If the maximum value is negative, use zero instead.
- To use the values of calculated sums optimally we use a deque to store the sums along with their indexes in an increasing order of the sums . We also pop the element from the back when its index goes out of the window k of current index i.
Time Complexity: O(N)
Space Complexity: O(K)
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