LeetCode-in-All

763. Partition Labels

Medium

You are given a string s. We want to partition the string into as many parts as possible so that each letter appears in at most one part.

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. 

Example 2:

Input: s = “eccbbbbdec”

Output: [10]

Constraints:

• 1 <= s.length <= 500
• s consists of lowercase English letters.

Solution

#include <vector>
#include <string>
#include <unordered_map>

class Solution {
public:
    std::vector<int> partitionLabels(const std::string& s) {
        std::vector<int> result;
        std::vector<int> position(26, 0);
        
        // Store the last position of each character
        for (int i = 0; i < s.size(); ++i) {
            position[s[i] - 'a'] = i;
        }
        
        int max = 0;
        int prev = -1;
        
        for (int i = 0; i < s.size(); ++i) {
            // Update max position of current character
            if (position[s[i] - 'a'] > max) {
                max = position[s[i] - 'a'];
            }
            
            // If current index reaches max, partition found
            if (i == max) {
                result.push_back(i - prev);
                prev = i;
            }
        }
        
        return result;
    }
};

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