Prefix Sum III: The Definition of Prefix Sum
Another typical prefix sum problem (O(n)-time, O(n)-space). Code is down below, cheers, ACC.
Number of Ways to Split Array - LeetCode
2270. Number of Ways to Split Array
Medium
You are given a 0-indexed integer array nums of length n.
nums contains a valid split at index i if the following are true:
- The sum of the first
i + 1elements is greater than or equal to the sum of the lastn - i - 1elements. - There is at least one element to the right of
i. That is,0 <= i < n - 1.
Return the number of valid splits in nums.
Example 1:
Input: nums = [10,4,-8,7] Output: 2 Explanation: There are three ways of splitting nums into two non-empty parts: - Split nums at index 0. Then, the first part is [10], and its sum is 10. The second part is [4,-8,7], and its sum is 3. Since 10 >= 3, i = 0 is a valid split. - Split nums at index 1. Then, the first part is [10,4], and its sum is 14. The second part is [-8,7], and its sum is -1. Since 14 >= -1, i = 1 is a valid split. - Split nums at index 2. Then, the first part is [10,4,-8], and its sum is 6. The second part is [7], and its sum is 7. Since 6 < 7, i = 2 is not a valid split. Thus, the number of valid splits in nums is 2.
Example 2:
Input: nums = [2,3,1,0] Output: 2 Explanation: There are two valid splits in nums: - Split nums at index 1. Then, the first part is [2,3], and its sum is 5. The second part is [1,0], and its sum is 1. Since 5 >= 1, i = 1 is a valid split. - Split nums at index 2. Then, the first part is [2,3,1], and its sum is 6. The second part is [0], and its sum is 0. Since 6 >= 0, i = 2 is a valid split.
Constraints:
2 <= nums.length <= 105-105 <= nums[i] <= 105
public int WaysToSplitArray(int[] nums)
{
long[] prefixSum = new long[nums.Length];
prefixSum[0] = nums[0];
for (int i = 1; i < nums.Length; i++) prefixSum[i] = nums[i] + prefixSum[i - 1];
int nWays = 0;
for (int i = 0; i < nums.Length - 1; i++)
{
if (prefixSum[i] >= prefixSum[prefixSum.Length - 1] - prefixSum[i]) nWays++;
}
return nWays;
}
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