66_Plus_One.java

class Solution {
    public int[] plusOne(int[] digits) {
        for (int i = digits.length - 1; i >= 0; i--) {
	        if (digits[i] < 9) {
		        digits[i]++;
		        return digits;
        // starting from extreme right--> if array[i] is less than 9 means can be added with 1
		// i.e. [ 5,8 ]-->[ 5,9 ] or
		//      [ 9,4 ]-->[ 9,5 ] or
		//      [ 6,0 ]-->[ 6,1 ]
		// and will directly return array
	        }
	    digits[i] = 0;
	// if array[i] is not less than 9, means it have to be 9 only then digit is changed to 0,
	// and we again revolve around loop to check for number if less than 9 or not
	// i.e. [ 5,9 ]-->[ 5,0 ]-loop->[ 6,0 ] or
	//      [ 1,9,9 ]-->[ 1,9,0 ]-loop->[ 1,0,0 ]-loop->[ 2,0,0 ]
	// and will directly return array
        }

// if all number inside array are 9
// i.e. [ 9,9,9,9 ] than according to above loop it will become [ 0,0,0,0 ]
// but we have to make it like this [ 9,9,9,9 ]-->[ 1,0,0,0,0 ]


// to make like above we need to make new array of length--> n+1
// by default new array values are set to -->0 only
// thus just changed first value of array to 1 and return the array

        digits = new int[digits.length + 1];
        digits[0] = 1;
        return digits;
    }
}