src/main/java/com/fishercoder/solutions/_307.java

package com.fishercoder.solutions;

/**
 * 307. Range Sum Query - Mutable
 *
 * Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

 The update(i, val) function modifies nums by updating the element at index i to val.
 Example:
 Given nums = [1, 3, 5]

 sumRange(0, 2) -> 9
 update(1, 2)
 sumRange(0, 2) -> 8
 Note:
 The array is only modifiable by the update function.
 You may assume the number of calls to update and sumRange function is distributed evenly.
 */
public class _307 {

	public static class Solution1 {
		class NumArray {
			class SegmentTreeNode {
				SegmentTreeNode left;
				SegmentTreeNode right;
				int start;
				int end;
				int sum;

				public SegmentTreeNode(int start, int end) {
					this.start = start;
					this.end = end;
					this.left = null;
					this.right = null;
					this.sum = 0;
				}
			}

			private SegmentTreeNode root = null;

			public NumArray(int[] nums) {
				root = buildSegmentTree(nums, 0, nums.length - 1);
			}

			SegmentTreeNode buildSegmentTree(int[] nums, int start, int end) {
				if (start > end) {
					return null;
				} else {
					SegmentTreeNode root = new SegmentTreeNode(start, end);
					if (start == end) {
						root.sum = nums[start];
					} else {
						int mid = start + (end - start) / 2;
						root.left = buildSegmentTree(nums, start, mid);
						root.right = buildSegmentTree(nums, mid + 1, end);
						root.sum = root.left.sum + root.right.sum;
					}
					return root;
				}
			}

			void update(int i, int val) {
				update(root, i, val);
			}

			void update(SegmentTreeNode root, int pos, int val) {
				if (root.start == root.end) {
					root.sum = val;
				} else {
					int mid = root.start + (root.end - root.start) / 2;
					if (pos <= mid) {
						update(root.left, pos, val);
					} else {
						update(root.right, pos, val);
					}
					root.sum = root.left.sum + root.right.sum;
				}
			}

			public int sumRange(int i, int j) {
				return sumRange(root, i, j);
			}

			int sumRange(SegmentTreeNode root, int start, int end) {
				if (root.end == end && root.start == start) {
					return root.sum;
				} else {
					int mid = root.start + (root.end - root.start) / 2;
					if (end <= mid) {
						return sumRange(root.left, start, end);
					} else if (start >= mid + 1) {
						return sumRange(root.right, start, end);
					} else {
						return sumRange(root.right, mid + 1, end) + sumRange(root.left, start, mid);
					}
				}
			}
		}
	}
}