ValidPartitionForArray.java

/**
 * You are given a 0-indexed integer array nums. You have to partition the array into one or more contiguous subarrays.
 *
 * We call a partition of the array valid if each of the obtained subarrays satisfies one of the following conditions:
 *
 * The subarray consists of exactly 2 equal elements. For example, the subarray [2,2] is good.
 * The subarray consists of exactly 3 equal elements. For example, the subarray [4,4,4] is good.
 * The subarray consists of exactly 3 consecutive increasing elements, that is, the difference between adjacent elements is 1. For example, the subarray [3,4,5] is good, but the subarray [1,3,5] is not.
 * Return true if the array has at least one valid partition. Otherwise, return false.
 *
 *
 *
 * Example 1:
 *
 * Input: nums = [4,4,4,5,6]
 * Output: true
 * Explanation: The array can be partitioned into the subarrays [4,4] and [4,5,6].
 * This partition is valid, so we return true.
 * Example 2:
 *
 * Input: nums = [1,1,1,2]
 * Output: false
 * Explanation: There is no valid partition for this array.
 *
 *
 * Constraints:
 *
 * 2 <= nums.length <= 105
 * 1 <= nums[i] <= 106
 */

class Solution {
    public boolean validPartition(int[] nums) {
        int n = nums.length;
        boolean[] dp = new boolean[n + 1];
        dp[0] = true;
        for(int i = 2; i <= n; i++){
            if(nums[i - 1] == nums[i - 2]) dp[i] = dp[i - 2];
            if(i > 2 && nums[i - 1] == nums[i - 2] && nums[i - 2] == nums[i - 3]) dp[i] |= dp[i - 3];
            if(i > 2 && nums[i - 1] == 1 + nums[i - 2]
                    && nums[i - 2] == 1 + nums[i - 3]) dp[i] |= dp[i - 3];
        }

        return dp[n];
    }
}