线段树 c++实现

#include
#include
using namespace std;

#define MAXSIZE  1000

void build_tree(int arr[], int tree[], int node, int start, int end){
    if(start == end){
        tree[node] = arr[start];
    }else{

        int mid = (start + end) / 2;
        int left = 2 * node +  1;
        int right  = 2 * node + 2;
        build_tree(arr, tree, left,start,mid );
        build_tree(arr, tree, right, mid + 1, end);
        tree[node] = tree[left] + tree[right];
    }

}

void update_tree(int arr[], int tree[], int node, int start, int end, int ind, int val){
    if(start == end){
        arr[ind] = val;
        tree[node] = val;
        return;
    }
    int mid = (start + end) / 2;
    int left = 2 * node + 1;
    int right = 2 * node + 2;
    if(ind >= start && ind <= mid){
        update_tree(arr, tree, left, start, mid, ind, val);
    }
    else{
        update_tree(arr, tree, right, mid + 1, end, ind, val);
    }
    tree[node] = tree[left] + tree[right];
}

// 树的每个节点代表的是数组一段区间的和

int qurry_tree(int arr[], int tree[], int node, int start, int end, int l, int r){
    cout << "start: " << start << " end: "<< end << endl;
    if(l > end || r < start)  return 0;
    // 会少返回一些节点吗？不会，包含在这棵子树内的所有数都返回了，其他数不在这棵子树里
    // 也就是说，所有的数都能找到唯一的归属，并且返回
    if(l<=start && r >=end){
        return tree[node];
    }
    if(start == end){
        return tree[node];
    }
    int mid = (start + end) / 2;
    int left  = 2 * node + 1;
    int right = 2 * node + 2;
    // 将[l...r] 分给两棵子树去查
    int sum_left = qurry_tree(arr, tree, left, start, mid, l, r);
    int sum_right = qurry_tree(arr, tree, right, mid + 1, end, l, r);
    return sum_left + sum_right;
}

int main(){
    int arr[] = {1,3,5,7,9,11};
    int size = 6;
    int tree[MAXSIZE] = {0};
    build_tree(arr,tree, 0, 0, size - 1);

    cout << endl;
    update_tree(arr, tree, 0, 0,size - 1, 4,6);

    int ans = qurry_tree(arr, tree, 0, 0, size -1, 2, 5);
    cout << "ans = " << ans << endl;
    return 0;
}