665. Non-decreasing Array

Input: [4,2,3]
Output: True
Explanation: You could modify the first 4 to 1 to get a non-decreasing array.

Input: [4,2,1]
Output: False
Explanation: You can't get a non-decreasing array by modify at most one element.

class Solution {
     public boolean checkPossibility(int[] nums) {
       if(nums.length<=1){
            return true;
        }
        
        List<Integer> list = new ArrayList<>();
        for(int i = 0;i<nums.length-1;i++){
           if(nums[i]>nums[i+1]){
               list.add(i+1);
           }
        }
        if(list.size()>1){
            return false;
        }
        if(list.size()== 0 || list.get(0)==1 || list.get(0)==nums.length-1){
            return true;
        }
        int left =0;
        for(int i = 0;i<list.get(0);i++){
            if(nums[i]>nums[list.get(0)]){
                left++;
            }
        }
        int right = 0;
        for (int i = list.get(0); i < nums.length; i++) {
            if(nums[i]<nums[list.get(0)-1]){
                right++;
            }
        }
        
        if(left >1 && right>1){
            return false;
        }
        return true;
    }
}

class Solution {
    public boolean checkPossibility(int[] nums) {
       int count = 0;
        for(int i = 0;i<nums.length -1 ;i++){
            if(nums[i]>nums[i+1]){
                count++;
                if(i>0 && nums[i+1]<nums[i-1]){
                    nums[i+1] = nums[i];
                }
            }
        }
        return count<=1;
    }
}