Problem could be found on Leetcode Here
Problem Description
Given a word, you need to judge whether the usage of capitals in it is right or not.
We define the usage of capitals in a word to be right when one of the following cases holds:
All letters in this word are capitals, like “USA”.
All letters in this word are not capitals, like “leetcode”.
Only the first letter in this word is capital, like “Google”.
Otherwise, we define that this word doesn’t use capitals in a right way.
Example 1:
Input: "USA"
Output: True
Example 2:
Input: "FlaG"
Output: False
Note: The input will be a non-empty word consisting of uppercase and lowercase latin letters.
My Solution
Code
public class Solution {
public bool DetectCapitalUse(string word) {
if(word == null) return false;
int ucount = 0;
bool l = false;
for(int i = 0; i < word.Length; i ++){
if(i > 0 && l){
if(Char.IsUpper(word[i])) return false;
}
if(ucount > 1 && Char.IsLower(word[i])) return false;
if(Char.IsUpper(word[i])){
ucount ++;
}
else{
l = true;
}
}
return true;
}
}
Explain
Time Complexity: O(n) - n is the length of the string.
All cases for us to pause the loop and return false could be inffered from the problem
-
Any lowercases followed by uppercase (case: aA)
-
If there are more than one uppercase letter inside the string, no lowercase should be found in the rest of the string
So I set a bool l to detect if there already existed lowercase letter in the string and a int ucount to count the number of uppercase letter in the string.
Failure Case Study
word = aBBBB
loop 1:
l = true, ncount = 0; Go to the next loop
loop 2:
l = true, B is an uppercase letter, matches failure case 1, return false
word = BBaa
loop 1:
l = false, ncount = 1; Go to the next loop
loop 2:
l = false, ncount = 2; Go to the next loop
loop 3:
ncount = 2; a is a lowercase letter, matches failure case 2, return false
