Description Link to heading

1144. Decrease Elements To Make Array Zigzag (Medium)

Given an array nums of integers, a move consists of choosing any element and decreasing it by 1.

An array A is a zigzag array if either:

  • Every even-indexed element is greater than adjacent elements, ie. A[0] > A[1] < A[2] > A[3] < A[4] > ...
  • OR, every odd-indexed element is greater than adjacent elements, ie. A[0] < A[1] > A[2] < A[3] > A[4] < ...

Return the minimum number of moves to transform the given array nums into a zigzag array.

Example 1:

Input: nums = [1,2,3]
Output: 2
Explanation: We can decrease 2 to 0 or 3 to 1.

Example 2:

Input: nums = [9,6,1,6,2]
Output: 4

Constraints:

  • 1 <= nums.length <= 1000
  • 1 <= nums[i] <= 1000

Solution Link to heading

Note that element can only be decreased by 1. Analog by case.

Code Link to heading 

class Solution {
  public:
    int movesToMakeZigzag(vector<int> &nums) {
        if (nums.size() == 1)
            return 0;
        int cnt2 = 0;
        for (int i = 1; i < nums.size(); i += 2) {
            if (i + 1 < nums.size() && i - 1 >= 0) {
                int tmp = std::min(nums[i + 1], nums[i - 1]);
                if (tmp <= nums[i]) {
                    cnt2 += nums[i] - tmp + 1;
                }
            } else if (i + 1 >= nums.size()) {
                if (nums[i - 1] <= nums[i]) {
                    cnt2 += nums[i] - nums[i - 1] + 1;
                }
            } else {
                if (nums[i + 1] <= nums[i]) {
                    cnt2 += nums[i] - nums[i + 1] + 1;
                }
            }
        }
        int cnt4 = 0;
        for (int i = 0; i < nums.size(); i += 2) {
            if (i + 1 < nums.size() && i - 1 >= 0) {
                int tmp = std::min(nums[i + 1], nums[i - 1]);
                if (tmp <= nums[i]) {
                    cnt4 += nums[i] - tmp + 1;
                }
            } else if (i + 1 >= nums.size()) {
                if (nums[i - 1] <= nums[i]) {
                    cnt4 += nums[i] - nums[i - 1] + 1;
                }
            } else {
                if (nums[i + 1] <= nums[i]) {
                    cnt4 += nums[i] - nums[i + 1] + 1;
                }
            }
        }
        return std::min(cnt2, cnt4);
    }
};