763. Partition Labels

Posted 2021-02-02 ruruozhenhao

A string S of lowercase letters is given. We want to partition this string into as many parts as possible so that each letter appears in at most one part, and return a list of integers representing the size of these parts.

 

Example 1:

Input: S = "ababcbacadefegdehijhklij"
Output: [9,7,8]
Explanation:
The partition is "ababcbaca", "defegde", "hijhklij".
This is a partition so that each letter appears in at most one part.
A partition like "ababcbacadefegde", "hijhklij" is incorrect, because it splits S into less parts.

 

Note:

1. S will have length in range [1, 500].
2. S will consist of lowercase letters (‘a‘ to ‘z‘) only.

 

Approach #1: C++.

class Solution {
public:
    vector<int> partitionLabels(string S) {
        int len = S.length();
        int curLen = 0;
        vector<int> ans;
        
        for (int i = 0; i < len; ++i) {
            curLen = helper(S, i);
            for (int j = i+1; j < curLen; ++j) {
                curLen = max(curLen, helper(S, j));
            }
            
            ans.push_back(curLen-i+1);
            i = curLen;
        }
        
        return ans;
    }
    
    int helper(string S, int index) {
        int curLen = index;
        int len = S.length();
        int temp;
        while (index >= 0) {
            curLen = index;
            index = S.find(S[curLen], curLen+1);
        }
        
        return curLen;
    }
};

　　

Analysis:

I use helper function to find the last index of current character. In the partitionLabels function we traversing the string and find the min interval.