An element x of an integer array arr of length m is dominant if more than half the elements of arr have a value of x.
You are given a 0-indexed integer array nums of length n with one dominant element.
You can split nums at an index i into two arrays nums[0, ..., i] and nums[i + 1, ..., n - 1], but the split is only valid if:
0 <= i < n - 1nums[0, ..., i], and nums[i + 1, ..., n - 1] have the same dominant element.Here, nums[i, ..., j] denotes the subarray of nums starting at index i and ending at index j, both ends being inclusive. Particularly, if j < i then nums[i, ..., j] denotes an empty subarray.
Return the minimum index of a valid split. If no valid split exists, return -1.
Example 1:
Input: nums = [1,2,2,2] Output: 2 Explanation: We can split the array at index 2 to obtain arrays [1,2,2] and [2]. In array [1,2,2], element 2 is dominant since it occurs twice in the array and 2 * 2 > 3. In array [2], element 2 is dominant since it occurs once in the array and 1 * 2 > 1. Both [1,2,2] and [2] have the same dominant element as nums, so this is a valid split. It can be shown that index 2 is the minimum index of a valid split.
Example 2:
Input: nums = [2,1,3,1,1,1,7,1,2,1] Output: 4 Explanation: We can split the array at index 4 to obtain arrays [2,1,3,1,1] and [1,7,1,2,1]. In array [2,1,3,1,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5. In array [1,7,1,2,1], element 1 is dominant since it occurs thrice in the array and 3 * 2 > 5. Both [2,1,3,1,1] and [1,7,1,2,1] have the same dominant element as nums, so this is a valid split. It can be shown that index 4 is the minimum index of a valid split.
Example 3:
Input: nums = [3,3,3,3,7,2,2] Output: -1 Explanation: It can be shown that there is no valid split.
Constraints:
1 <= nums.length <= 1051 <= nums[i] <= 109nums has exactly one dominant element.class Solution {
public int minimumIndex(List<Integer> nums) {
// Find dominant element (mode)
Map<Integer, Integer> freq = new HashMap<>();
int n = nums.size(), maxCount = 0, mode = -1;
for (int i : nums) {
freq.put(i, freq.getOrDefault(i, 0) + 1);
if (freq.get(i) > maxCount) {
maxCount = freq.get(i);
mode = i;
}
}
// Compute dominant element counts prefix sum
int prefixSum = 0;
for (int i = 0; i < n; i++) {
if (nums.get(i) == mode)
prefixSum++;
// System.out.println(i + 1 + "\t" + prefixSum);
if ((i+1) / 2 < prefixSum && (n - 1 - i) / 2 < (maxCount - prefixSum))
return i;
}
return -1;
}
}