Problems 168, 171, 205, 387 Added

Author: omprashantjain

3 Strings/168 Excel Sheet Column Title.java

@@ -0,0 +1,13 @@
+class Solution {
+  public String convertToTitle(int columnNumber) {
+    StringBuilder result = new StringBuilder();
+    while (columnNumber > 0) {
+      columnNumber--;
+      int rem = columnNumber % 26;
+      char c = (char) ('A' + rem);
+      result.insert(0, c);
+      columnNumber /= 26;
+    }
+    return result.toString();
+  }
+}

3 Strings/171 Excel Sheet Column Number.java

@@ -0,0 +1,12 @@
+class Solution {
+  public int titleToNumber(String columnTitle) {
+    int result = 0;
+    int len = columnTitle.length();
+    for (int i = len - 1, pow = 0; i >= 0; i--, pow++) {
+      char c = columnTitle.charAt(i);
+      int digit = c - 'A' + 1;
+      result += digit * Math.pow(26, pow);
+    }
+    return result; 
+  }
+}

3 Strings/205 Isomorphic Strings.java

@@ -0,0 +1,24 @@
+import java.util.HashMap;
+
+class Solution {
+  public boolean isIsomorphic(String s, String t) {
+    if (s.length() != t.length()) {
+      return false;
+    }
+    HashMap<Character, Character> sToT = new HashMap<>();
+    HashMap<Character, Character> tToS = new HashMap<>();
+    for (int i = 0; i < s.length(); i++) {
+      char sChar = s.charAt(i);
+      char tChar = t.charAt(i);
+
+      if (sToT.getOrDefault(sChar, tChar) != tChar ||
+          tToS.getOrDefault(tChar, sChar) != sChar) {
+        return false;
+      }
+
+      sToT.put(sChar, tChar);
+      tToS.put(tChar, sChar);
+    }
+    return true;
+  }
+}