class NumArray {
int[] dp;
int len;
public NumArray(int[] nums) {
if (nums == null || nums.length == 0) return ;
len = nums.length;
dp = new int[len + 1];
for (int i = 1; i <= len; i++) {
dp[i] = dp[i - 1] + nums[i - 1];
}
}
public void update(int i, int val) {
int removeNum = dp[i + 1] - dp[i];
for (int k = i + 1; k <= len; k++) {
dp[k] = dp[k] - removeNum + val;
}
}
public int sumRange(int i, int j) {
return dp[j + 1] - dp[i];
}
}
/**
* 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);
*/
Here we implement a new data structure called Segment Tree:
public class NumArray {
class SegmentTreeNode {
int start, end;
SegmentTreeNode left, right;
int sum;
public SegmentTreeNode(int start, int end) {
this.start = start;
this.end = end;
this.left = null;
this.right = null;
this.sum = 0;
}
}
SegmentTreeNode root = null;
public NumArray(int[] nums) {
root = buildTree(nums, 0, nums.length-1);
}
private SegmentTreeNode buildTree(int[] nums, int start, int end) {
if (start > end) {
return null;
} else {
SegmentTreeNode ret = new SegmentTreeNode(start, end);
if (start == end) {
ret.sum = nums[start];
} else {
int mid = start + (end - start) / 2;
ret.left = buildTree(nums, start, mid);
ret.right = buildTree(nums, mid + 1, end);
ret.sum = ret.left.sum + ret.right.sum;
}
return ret;
}
}
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);
}
public 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);
}
}
}
}
Here is prefix sum solution(runtime beats 17%):
Here we implement a new data structure called Segment Tree: