feat : longest-substring-without-repeating-characters

Author: ekgns33

longest-substring-without-repeating-characters/ekgns33.java

@@ -0,0 +1,66 @@
+/**
+ input : String s
+ output: length of the longest substring without repeating chararcters
+
+ example)
+
+ abccba >> abc, cba >> 3
+ abcdeffg >> abcdef >> 6
+ constraints
+ 1) length of string s?
+ [0, 5 * 10^4]
+ 2) alphanumeric characters?
+ english, digit, symbol, space. >> 256 ascii characters
+  else >> hashmap
+
+ solution1)
+
+ iterate through string from index i = 0 to n-1
+ iterate through string s from index j = i + 1, j to n
+ if duplicate character comes up, then compare length
+ tc : O(n^2)
+ sc : O(1)
+
+ solution 2) sliding window
+
+ ds : array or hashmap << when character range is ascii, we can use array instead
+
+ use two pointer l and r
+ read until there is no repeating character in range [l, r]
+ if duplicate exists
+ move l until every character is unique
+ ex)
+
+ abaabcdef
+ l
+ r
+ ^^    ^
+ tc : O(n)
+ sc : O(1)
+
+
+ */
+
+class Solution {
+  public int lengthOfLongestSubstring(String s) {
+    int[] freq = new int[256];
+    int l = 0, r = 0;
+    int n = s.length();
+    int maxLength = 0;
+    if(n <= 1) return n;
+
+    while(r < n && l <= r) {
+      char curC = s.charAt(r);
+      freq[curC]++;
+      while(l < r && freq[curC] > 1) {
+        char prevC = s.charAt(l);
+        freq[prevC]--;
+        l++;
+      }
+      maxLength = Math.max(maxLength, r - l + 1);
+      r++;
+    }
+    maxLength = Math.max(maxLength, r- l);
+    return maxLength;
+  }
+}