Create #306 Additive Number.java

Author: zhmuch

#306 Additive Number.java

@@ -0,0 +1,62 @@
+//  Some bugs;
+
+
+import java.util.*;
+
+public class Solution {
+
+    String num;
+
+    public boolean isAdditiveNumber(String num) {
+
+        if(num == null || num.length() < 3)
+            return false;
+
+        this.num = num;
+        int max = Math.min(num.length() / 2, 9);
+
+        for(int i = 0; i < max; i++)
+            for(int j = 0; j < max; j++){
+                int prepre = Integer.parseInt(num.substring(0, i + 1));
+                int pre = Integer.parseInt(num.substring(i + 1, i + j + 2));
+                if(dfs(prepre, pre, Math.max(i, j) + 1, i + j + 2))
+                    return true;
+            }
+
+        return false;
+    }
+
+    private boolean dfs(int prepre, int pre, int digits, int idx) {
+        
+        // System.out.println(prepre + "  " + pre + "  " + digits + "  " + idx);
+        
+        if(idx >= num.length())
+            return true;
+        
+        if(num.charAt(idx) == '0' && digits > 1)
+            return false;
+
+        if(num.length() - idx < digits)
+            return false;
+        
+        boolean res = false;
+        
+        //  digits
+        int pos = Integer.parseInt(num.substring(idx, idx + digits));
+        if(pos == prepre + pre)
+            res = dfs(pre, pos, digits, idx + digits);
+        
+        if(res)
+            return res;
+        
+        //  digits + 1;
+        if(idx + digits + 1 <= num.length() && digits < 9){
+            int poss = Integer.parseInt(num.substring(idx, idx + digits + 1));
+            if(poss == prepre + pre)
+                res = dfs(pre, poss, digits + 1, idx + digits + 1);
+        }
+        
+        
+        return res;
+    }
+}