NumArray.java

import jdk.javadoc.internal.doclets.formats.html.SourceToHTMLConverter;

class NumArray {

    int[] tree;
    int n;

    public NumArray(int[] nums) {
        if (nums.length > 0) {
            n = nums.length;
            tree = new int[n * 2];
            buildTree(nums);
        }
    }

    private void buildTree(int[] nums) {
        for (int i = n, j = 0; i < 2 * n; i++, j++)
            tree[i] = nums[j];
        for (int i = n - 1; i > 0; --i)
            tree[i] = tree[i * 2] + tree[i * 2 + 1];
    }

    public void update(int pos, int val) {
        pos += n;
        tree[pos] = val;
        while (pos > 0) {
            int left = pos;
            int right = pos;
            if (pos % 2 == 0) {
                right = pos + 1;
            } else {
                left = pos - 1;
            }
            // parent is updated after child is updated
            tree[pos / 2] = tree[left] + tree[right];
            pos /= 2;
        }
    }

    public int sumRange(int l, int r) {
        // get leaf with value 'l'
        l += n;
        // get leaf with value 'r'
        r += n;
        int sum = 0;
        while (l <= r) {
            if ((l % 2) == 1) {
                sum += tree[l];
                l++;
            }
            if ((r % 2) == 0) {
                sum += tree[r];
                r--;
            }
            l /= 2;
            r /= 2;
        }
        return sum;
    }
    public static void main(String[] args) {
        int[] nums = {1, 3, 5};
        NumArray na = new NumArray(nums);
        na.printArray();
        na.sumRange(0, 2);
    }

    public void printArray() {
        for (int i = 0; i < tree.length; i++) {
            System.out.println(tree[i]);
        }
    }
}

/**
 * Your NumArray object will be instantiated and called as such: NumArray obj =
 * new NumArray(nums); obj.update(index,val); int param_2 =
 * obj.sumRange(left,right);
 */