Record last index; Iterate from front to find if i == end for current interval

Author: GuanhuiGuan

Partition Labels.java

@@ -0,0 +1,67 @@
+class Solution {
+    // O(n)
+    public List<Integer> partitionLabels(String S) {
+        // record the last index of each character
+        // sweep and record when i == end(max end of current interval)
+        if(S == null || S.length() == 0) return new ArrayList<>();
+        
+        int[] map = new int[26];
+        for(int i = 0; i < S.length(); i++) {
+            map[S.charAt(i) - 'a'] = i;
+        }
+        int start = 0, end = 0;
+        List<Integer> res = new ArrayList<>();
+        for(int i = 0; i < S.length(); i++) {
+            end = Math.max(end, map[S.charAt(i) - 'a']);
+            if(i == end) {
+                res.add(end - start + 1);
+                start = end + 1;
+            }
+        }
+        return res;
+    }
+    
+    
+//     // O(nlogn)
+//     public List<Integer> partitionLabels(String S) {
+//         Map<Character, int[]> map = new HashMap<>();
+//         for(int i = 0; i < S.length(); i++) {
+//             char c = S.charAt(i);
+//             int[] expand = new int[] {i, i};
+//             if(map.containsKey(c)) {
+//                 expand = map.get(c);
+//                 expand[1] = i;
+//             }
+//             map.put(c, expand);
+//         }
+        
+//         List<int[]> intervals = new ArrayList<>(map.values());
+//         intervals.sort(new Comparator<int[]>() {
+//             @Override
+//             public int compare(int[] i1, int[] i2) {
+//                 return i1[0] == i2[0]? i1[1] - i2[1] : i1[0] - i2[0];
+//             }
+//         });
+        
+//         List<Integer> res = new ArrayList<>();
+//         if(intervals.isEmpty()) return res;
+//         int start = -1, end = -1;
+//         for(int[] interval: intervals) {
+//             if(end == -1) {
+//                 start = interval[0];
+//                 end = interval[1];
+//             }
+//             else if(end >= interval[0]) {
+//                 start = Math.min(start, interval[0]);
+//                 end = Math.max(end, interval[1]);
+//             }
+//             else {
+//                 res.add(end - start + 1);
+//                 start = interval[0];
+//                 end = interval[1];
+//             }
+//         }
+//         res.add(end - start + 1);
+//         return res;
+//     }
+}