Solved 3 problems

varunu28 · varunu28 · commit fb41c61e857a · 2017-12-06T13:29:42.000-08:00
diff --git a/Easy/Count Primes.java b/Easy/Count Primes.java
@@ -0,0 +1,23 @@
+class Solution {
+    public int countPrimes(int n) {
+        int[] arr = new int[n];
+        
+        for (int i=2;i<n;i++) {
+            if (arr[i] != 1) {            
+                for (int j = i*2;j<n;j+=i) {
+                    arr[j] = 1;
+                }
+            } 
+            else {
+                arr[i] = 1;
+            }
+        }
+        
+        int count = 0;
+        for (int i=2;i<n;i++) {
+            if (arr[i] == 0) count++;
+        }
+        
+        return count;
+    }
+}
diff --git a/Easy/Roman to Integer.java b/Easy/Roman to Integer.java
@@ -0,0 +1,39 @@
+class Solution {
+    public int romanToInt(String s) {
+        String symbol = "IVXLCDM";
+        int[] val = {1, 5, 10, 50, 100, 500, 1000};
+        
+        char[] s_char = s.toCharArray();
+        
+        int[] s_val = new int[s_char.length];
+        
+        for (int i=0;i<s_char.length;i++) {
+            s_val[i] = val[symbol.indexOf(s_char[i])];
+        }
+        
+        int total = 0;
+        int k = 0;
+        
+        while (k < s_val.length) {
+            int s1  = s_val[k];
+            if (k+1 < s_val.length) {
+                int s2 = s_val[k+1];
+                
+                if (s1 >= s2) {
+                    total += s1;
+                    k++;
+                }
+                else{
+                    total += s2-s1;
+                    k += 2;
+                }
+            }
+            else {
+                total += s1;
+                k++;
+            }
+        }
+        
+        return total;
+    }
+}
diff --git a/Easy/Valid Palindrome II.java b/Easy/Valid Palindrome II.java
@@ -0,0 +1,29 @@
+class Solution {
+    public boolean validPalindrome(String s) {
+        if (isPalindrome(s)) return true;        
+    
+        int i=0;
+        int j = s.length()-1;
+         
+        while (i<j && s.charAt(i) == s.charAt(j)) {
+            i++;
+            j--;
+        }
+        
+        if (i>=j) {
+            return true;
+        }
+        
+        if (isPalindrome(s.substring(i+1,j+1)) || isPalindrome(s.substring(i,j))) {
+            return true;
+        }
+        
+        return false;
+    }
+    
+    public boolean isPalindrome(String s) {
+        StringBuilder sb = new StringBuilder("");
+        sb.append(s);
+        return s.equals(sb.reverse().toString());
+    }
+}
