[Function add]

1. Add leetcode solutions.

Author: Seanforfun

README.md

@@ -475,6 +475,12 @@
 
 [304. Range Sum Query 2D - Immutable](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/304.%20Range%20Sum%20Query%202D%20-%20Immutable.md)
 
+[305. Number Of Island II](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/305.%20Number%20Of%20Island%20II.md)
+
+[306. Additive Number](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/306.%20Additive%20Number.md)
+
+[307. Range Sum Query - Mutable](https://github.com/Seanforfun/Algorithm-and-Leetcode/blob/master/leetcode/307.%20Range%20Sum%20Query%20-%20Mutable.md)
+
 
 ## Algorithm(4th_Edition)
 Reading notes of book Algorithm(4th Algorithm),ISBN: 9787115293800.

leetcode/306. Additive Number.md

@@ -1,3 +1,11 @@
+---
+layout: post
+title:  "306. Additive Number"
+date:   2019-03-03 17:37
+author: Botao Xiao
+categories: Leetcode
+description:
+---
 ## 306. Additive Number
 
 ### Question
@@ -59,4 +67,34 @@ class Solution {
         }
     }
 }
+```
+
+### Second time
+```Java
+class Solution {
+    public boolean isAdditiveNumber(String num) {
+        boolean result = false;
+        for(int i = 1; i <= num.length() - 2; i++){
+            for(int j = i + 1; j <= num.length() - 1; j++){
+                if(i != 1 && num.substring(0, i).startsWith("0")) continue;
+                if(j - i != 1 && num.substring(i, j).startsWith("0")) continue;
+                result |= backtrace(num, Long.parseLong(num.substring(0, i)), Long.parseLong(num.substring(i, j)), j);
+            }
+        }
+        return result;
+    }   
+    
+    private boolean backtrace(String num, long first, long second, int idx){
+        if(idx >= num.length()) return true;
+        long sum = first + second;
+        if(sum != 0 && num.substring(idx).startsWith("0")) return false;
+        else{
+            boolean temp = false;
+            if(num.substring(idx).startsWith("" + sum)){
+                temp |= backtrace(num, second, sum, idx + ("" + sum).length());
+            }
+            return temp;
+        }
+    }
+}
 ```

leetcode/307. Range Sum Query - Mutable.md

@@ -74,6 +74,60 @@ class NumArray {
     }
 }
 
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * NumArray obj = new NumArray(nums);
+ * obj.update(i,val);
+ * int param_2 = obj.sumRange(i,j);
+ */
+```
+
+### Second time
+1. Use binary index tree
+```Java
+class NumArray {
+    private int[] c;
+    private int[] nums;
+    private int lowBit(int n){
+        return n & (-n);
+    }
+    public NumArray(int[] nums) {
+        c = new int[nums.length + 1];
+        this.nums = nums;
+        for(int i = 1; i <= nums.length; i++){
+            int lowBit = lowBit(i);
+            int sum = 0;
+            for(int j = i - lowBit + 1; j <= i; j++){
+                sum += nums[j - 1];
+            }
+            c[i] = sum;
+        }
+    }
+    public void update(int i, int val) {
+        int diff = val - nums[i];
+        nums[i] = val;
+        int index = i + 1;
+        while(index <= this.nums.length){
+            c[index] += diff;
+            index += lowBit(index);
+        }
+    }
+    public int sumRange(int i, int j) {
+        int sum1 = 0;
+        int index1 = i;
+        while(index1 > 0){
+            sum1 += c[index1];
+            index1 -= lowBit(index1);
+        }
+        int sum2 = 0;
+        int index2 = j + 1;
+        while(index2 > 0){
+            sum2 += c[index2];
+            index2 -= lowBit(index2);
+        }
+        return sum2 - sum1;
+    }
+}
 /**
  * Your NumArray object will be instantiated and called as such:
  * NumArray obj = new NumArray(nums);