763.划分字母区间

class Solution {
public:
    vector<int> partitionLabels(string s) {
        int v[26] = {0};
        vector<int> res;
        for (int i = 0; i < s.size(); i ++ ) {
            v[s[i]-'a']=i;
        }
        int last = v[s[0]-'a'];
        int pre = 0;
        for (int i = 0; i < s.size(); i ++ ) {
            last = max(last,v[s[i]-'a']);
            if (last == i) {
                res.push_back(i - pre + 1);
                pre = i + 1;
            }
        }
        return res;
    }
};