Created
May 22, 2017 05:46
-
-
Save BiruLyu/dd7699e1d5ef9e9d56b006d85e9da0e6 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
public class NumArray { | |
private int[] nums; | |
private int[] BITree; | |
public NumArray(int[] nums) { | |
int len = nums.length; | |
this.nums = nums; | |
this.BITree = new int[len + 1]; | |
for( int i = 0; i < len; i++){ | |
initBITree(i, nums[i]); | |
} | |
} | |
public void initBITree(int i, int val){ | |
int idx = i + 1; | |
while( idx < this.BITree.length){ | |
this.BITree[idx] += val; | |
idx += idx & (-idx); | |
} | |
} | |
public void update(int i, int val) { | |
int len = this.nums.length; | |
int diff = val - this.nums[i]; | |
this.nums[i] = val;//updated the nums[i], otherwise the calculated diff became wrong upating the same index next time | |
initBITree(i, diff); | |
} | |
public int getSum(int i){ | |
int sum = 0; | |
i = i + 1; | |
while(i > 0){ | |
sum += this.BITree[i]; | |
i -= i & (-i); | |
} | |
return sum; | |
} | |
public int sumRange(int i, int j) { | |
//return this.BITree[j]; | |
return getSum(j) - getSum(i - 1); | |
} | |
} | |
/** | |
* 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); | |
*/ |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment