I've written a function that searches for the nth occurrence of a character in the given string. A positive value for n will search from left-to-right, while a negative value will search from right-to-left. Zero is not a valid value for n.
Left-to-Right Search
"AABAXYAMN".NthIndexOf('A', 1) -> 0
"AABAXYAMN".NthIndexOf('A', 2) -> 1
"AABAXYAMN".NthIndexOf('A', 3) -> 3
Right-to-Left Search
"AABAXYAMN".NthIndexOf('A', -1) -> 6
"AABAXYAMN".NthIndexOf('A', -2) -> 3
"AABAXYAMN".NthIndexOf('A', -3) -> 1
Original CodeCode:
/// <summary>
/// Searches for the nth occurrence of a character in the given string. A positive value for n will search from
/// left-to-right while a negative value will search from right-to-left. Zero is not a valid value for n.
/// </summary>
public static int NthIndexOf(this string input, char charToFind, int n) {
int position;
switch (Math.Sign(n)) {
case 1:
position = 0;
while (((position = input.IndexOf(charToFind, position)) != -1) && ((--n) > 0)) { position++; }
break;
case -1:
position = input.Length - 1;
while (((position = input.LastIndexOf(charToFind, position)) != -1) && ((++n) < 0)) { position--; }
break;
default:
throw new ArgumentOutOfRangeException(message: "param cannot be equal to 0", paramName: nameof(n));
}
return position;
}
Current Code: https://gist.github.com/Kittoes/904e785cc3a2b4d4d0da8694389179b8
