Method NumArray

java/0307-range-sum-query-mutable.java:5–9

(int[] nums)

    public int[] tree;

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

    // O(n)
    private void buildTree(int[] nums) {