307号问题
来源:1-6 线段树中的更新操作
ForeverLovel
2021-01-30 12:12:37
class NumArray {
private interface Merger<E> {
E merge(E a, E b);
}
private class SegmentTree<E> {
private E[] tree;
private E[] data;
private Merger<E> merger;
public SegmentTree(E[] arr, Merger<E> merger) {
this.merger = merger;
data = (E[]) new Object[arr.length];
for (int i = 0; i < arr.length; i++)
data[i] = arr[i];
tree = (E[])new Object[4 * arr.length];
buildSegmentTree(0,0, data.length - 1);
}
//在treeIndex的位置创建表示区间[l...r]的线段树
private void buildSegmentTree(int treeIndex, int l, int r){
if (l == r){
tree[treeIndex] = data[l];
return;
}
int leftTreeIndex = leftChild(treeIndex);
int rightTreeIndex = rightChild(treeIndex);
int mid = l + (r - l) / 2;
buildSegmentTree(leftTreeIndex,l,mid);
buildSegmentTree(rightTreeIndex, mid + 1, r);
tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
}
public int getSize(){
return data.length;
}
public E get(int index){
if(index < 0 || index >= data.length)
throw new IllegalArgumentException("Index is illegal");
return data[index];
}
public int leftChild(int index){
return 2 * index + 1;
}
public int rightChild(int index){
return 2 * index + 2;
}
public E query(int queryL, int queryR){
if(queryL < 0 || queryL >= data.length || queryR < 0 || queryR >= data.length || queryL > queryR)
throw new IllegalArgumentException("index is illegal");
return query(0, 0, data.length - 1, queryL, queryR);
}
private E query(int treeIndex, int l, int r, int queryL, int queryR){
if (l == queryL && r == queryR)
return tree[treeIndex];
int leftTreeIndex = leftChild(treeIndex);
int rightTreeIndex = rightChild(treeIndex);
int mid = l + (r - l) / 2;
if(queryL >= mid + 1)
return query(rightTreeIndex, mid + 1, r, queryL,queryR);
else if( queryR <= mid)
return query(leftTreeIndex,l,mid,queryL,queryR);
E leftRes = query(leftTreeIndex, l, mid, queryL, mid);
E rightRes = query(rightTreeIndex, mid + 1, r, mid + 1, queryR);
return merger.merge(leftRes, rightRes);
}
public void set(int index, E e){
if(index < 0 || index >= data.length)
throw new IllegalArgumentException("Index is illegal");
data[index] = e;
set(0, 0, data.length, index, e);
}
private void set(int treeIndex, int l, int r, int index, E e){
if(l == r){
tree[treeIndex] = e;
return;
}
int leftTreeIndex = leftChild(treeIndex);
int rightTreeIndex = rightChild(treeIndex);
int mid = l + (r - l) / 2;
if(index >= mid + 1)
set(rightTreeIndex, mid + 1,r,index,e);
else
set(leftTreeIndex,l, mid,index,e);
tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
}
@Override
public String toString(){
StringBuilder res = new StringBuilder();
res.append("[");
for (int i = 0; i < tree.length; i++){
if (tree[i] != null)
res.append(tree[i]);
else
res.append("null");
if( i != tree.length - 1)
res.append(", ");
}
res.append("]");
return res.toString();
}
}
private SegmentTree<Integer> segTree;
public NumArray(int[] nums){
if(nums.length != 0){
Integer[] data = new Integer[nums.length];
for (int i = 0; i < nums.length; i++){
data[i] = nums[i];
}
segTree = new SegmentTree<>(data, (a, b) -> a + b);
}
}
public void update(int index, int val){
if(segTree == null)
throw new IllegalArgumentException("segment tree is null");
segTree.set(index, val);
}
public int sumRange(int i, int j){
if( segTree ==null )
throw new IllegalArgumentException("segment tree is null");
return segTree.query(i, j);
}
}
/**
* 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);
*/
提交leetcode报空指针错误 在segTree初始化那
2回答
Mosea
2023-09-06
这里写错了,应该是set(0,0,data.length-1,index,e);
liuyubobobo
2021-01-30
我测试了一下,把课程这里的线段树代码替换掉你的线段树代码,没有问题:https://git.imooc.com/class-105/Play-Algorithms-and-Data-Structures/src/master/22-Segment-Tree/06-Update-Single-Element-in-Segment-Tree/src/SegmentTree.java
说明你的线段树代码实现有问题。请根据课程代码,调试比对,看自己的代码哪里有问题。
对于出问题的测试用例,Leetcode 会给出能复现错误的用例,请在本地尝试运行错误的用例,进行调试。进步就在这个过程中哦。
加油!:)
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