Cavity map

[pattrick128]

This is a coding question on Hackerrank.

We're given a bunch of strings of ints, say 1112, 1234, and 1842. If a certain digit in the string is bigger than both its neighbors, we will replace that digit with an 'X'. (In this case, 1842 -> 1X42) Clearly, the first and last digit will have nothing happen to them since they don't have a second neighbor to compare to.

I stored these strings of ints into a vector, and I have a check for the first and last digit in the string. If we're working with the string of ints "1842", I have two checks: 1. last digit will have no neighbor after it, so I'm checking for the value at k+1 -> if it's null, then do nothing to the digit. 2. same thing with first digit, if there's nothing before it at k-1, do nothing.

//loop through each individual digit of each string (in this case, 4 digits per string)
        for (int k = 0; k < st.length(); k++) {
            //if the variable is at edge, move on to the next int
            if (v.at(k+1) == null || v.at(k-1) == null) {
                break;
            }

The compiler is complaining that "null" is not declared. I do have #include <cstddef> in the header. Is there any other way I can go about this?

[ResidentBiscuit]

You could just iterate from index 1 to size - 1

[pattrick128]

I ran into another problem, actually.

        //loop through each individual digit of each string (in this case, 4 digits per string)
        //starting from 1 to length-1 to avoid the edges, which we don't care about
        for (int k = 1; k < st.length()-1; k++) {
            //if current is greater than both neighbors, change that to 'X'
            if (st.at(k) > st.at(k+1) && st.at(k) > st.at(k-1)) {
                st.at(k) = 'X'; //replace that digit with an 'X'
            }
        }
        
        cout << st << endl;

When I'm testing this against 12121212121, the returned output is "214X4X3X47", when it should be "12X2X2X2X21". I'm assuming that output is the maximum integer value "2147483647". Why's that?