408. Valid Word Abbreviation

A string can be abbreviated by replacing any number of non-adjacent, non-empty substrings with their lengths. The lengths should not have leading zeros.

For example, a string such as "substitution" could be abbreviated as (but not limited to):

• "s10n" ("s ubstitutio n")
• "sub4u4" ("sub stit u tion")
• "12" ("substitution")
• "su3i1u2on" ("su bst i t u ti on")
• "substitution" (no substrings replaced)

The following are not valid abbreviations:

• "s55n" ("s ubsti tutio n", the replaced substrings are adjacent)
• "s010n" (has leading zeros)
• "s0ubstitution" (replaces an empty substring)

Given a string word and an abbreviation abbr

A substring is a contiguous non-empty sequence of characters within a string.

class Solution {
public:
    bool validWordAbbreviation(string word, string abbr) {
        int i = 0, j = 0;
        for(; i < word.size() and j < abbr.size();) {
            if(isdigit(abbr[j])) {
                if(abbr[j] == '0') return false;
                int num = 0;
                while(j < abbr.size() and isdigit(abbr[j])) {
                    num = num * 10 + abbr[j++] - '0';
                    if(i + num > word.size()) return false;
                }
                i += num;
            } else {
                if(word[i] != abbr[j]) return false;
                i++,j++;
            }
        }
        return i == word.size() and j == abbr.size();
    }
};