A string `S` of lowercase English 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:

• `S` will have length in range `[1, 500]`.
• `S` will consist of lowercase English letters (`'a'` to `'z'`) only.

Idea:

• Create hash table to track the last index of the letter
• use start and end variable to decide the partition letters
• when end reach to the last index of the letter :
• store the length of the partition letters (end – start + 1)
• reset start => end + 1

Solution:

``````/**
* @param {string} S
* @return {number[]}
*/
var partitionLabels = function(S) {
let last_index = new Map();
for (let i = 0; i < S.length; i++) {
last_index.set(S[i],  i);
}
let res = [];
let start = 0;
let end = 0;
for (let i = 0; i < S.length; i++) {
end = Math.max(end, last_index.get(S[i]));
if (i === end) {
res.push(end - start + 1);
start = end + 1;
}
}
return res;
};``````