线段树的表示如下,图中树的值表示区间值得和,线段树的表示和堆的表示方法相同。
代码
#include <stdio.h>
#define MAX_LEN 1000
void build_tree(int arr[], int tree[], int node, int start, int end) {
if (start == end) {
tree[node] = arr[start];
return;
}
int mid = start + (end - start) / 2;
int left_node = node * 2 + 1;
int right_node = node * 2 + 2;
build_tree(arr, tree, left_node, start, mid);
build_tree(arr, tree, right_node, mid + 1, end);
tree[node] = tree[left_node] + tree[right_node];
}
void update_tree(int arr[], int tree[], int node, int start, int end, int idx, int val) {
if (start == end) {
arr[idx] = val;
tree[node] = val;
return;
}
int mid = start + (end - start) / 2;
int left_node = node * 2 + 1;
int right_node = node * 2 + 2;
if (idx >= start && idx <= mid)
update_tree(arr, tree, left_node, start, mid, idx, val);
else
update_tree(arr, tree, right_node, mid + 1, end, idx, val);
tree[node] = tree[left_node] + tree[right_node];
}
int query_tree(int arr[], int tree[], int node, int start, int end, int L, int R) {
if (R<start || L > end)
return 0;
else if (L <= start && end <= R)
return tree[node];
else if (start == end)
return tree[node];
int mid = start + (end - start) / 2;
int left_node = node * 2 + 1;
int right_node = node * 2 + 2;
int sum_left = query_tree(arr, tree, left_node, start, mid, L, R);
int sum_right = query_tree(arr, tree, right_node, 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[MAX_LEN] = { 0 };
build_tree(arr, tree, 0, 0, size - 1);
for (int i = 0; i < 15; i++)
printf("tree[%d]=%d\n", i, tree[i]);
printf("\n");
update_tree(arr, tree, 0, 0, size - 1, 4, 6);
for (int i = 0; i < 15; i++)
printf("tree[%d]=%d\n", i, tree[i]);
int s = query_tree(arr, tree, 0, 0, size - 1, 2, 5);
printf("%d\n", s);
return 0;
}