HDU 1754 解题报告 线段树 单点更新

线段树入门题，单点更新。每个结点存储两个孩子最大者即可。

//线段树单点更新，完全二叉树解法#include <cstdio>#define MAXN 200000#define lson rt<<1#define rson rt<<1|1int top[MAXN * 4 + 100];int students[MAXN + 10];int k;void pushup(int rt){top[rt] = top[lson] > top[rson] ? top[lson] : top[rson];}void build(int rt, int l, int r){if (l == r) {scanf("%d", &k);top[rt] = k;}else {int mid = (l + r) / 2;build(lson, l, mid);build(rson, mid+1, r);pushup(rt);}}void add(int rt, int l, int r, int node, int num){if (l == r) {top[rt] = num;}else {int mid = (l + r) / 2;if (node <= mid) {add(lson, l, mid, node, num);}else {add(rson, mid+1, r, node, num);}pushup(rt);}}int query(int rt, int l, int r, int ll, int rr){if (l == ll && r == rr) {return top[rt];}else {int mid = (l + r) / 2;if (rr <= mid) return query(lson, l, mid, ll, rr);else if (mid < ll) return query(rson, mid+1, r, ll, rr);else {//注意最后两个参数也要做相应的变动int a = query(lson, l, mid, ll, mid); int b = query(rson, mid+1, r, mid+1, rr);return a > b ? a : b;}}}int main(){//freopen("testdata/1754.txt", "r", stdin);int n, m, left, right;char c;while (scanf("%d %d", &n, &m) != EOF) {build(1, 1, n);for (int i = 0; i < m; ++i) {getchar();scanf("%c %d %d", &c, &left, &right);if (c == 'Q') {printf("%d\n", query(1, 1, n, left, right));}else if (c == 'U') {add(1, 1, n, left, right);}}}return 0;}