HDOJ 1754 I Hate It（线段树基本操作）

思路：

线段树的基本操作：单点替换，区间最值

#include <cstdio> #include <cstdlib> #include <cstring> #include <algorithm> using namespace std; #define lhs l, m, rt << 1 #define rhs m + 1, r, rt << 1 | 1  const int maxn = 200010; int seg[maxn << 2]; void pushUp(int rt) {

    seg[rt] = max(seg[rt << 1], seg[rt << 1 | 1]); } void build(int l, int r, int rt) { if (l == r) {

        scanf("%d", &seg[rt]); return; } int m = (l + r) >> 1;

    build(lhs);

    build(rhs);

    pushUp(rt); } void update(int p, int delta, int l, int r, int rt) { if (l == r) {

        seg[rt] = delta; return; } int m = (l + r) >> 1; if (p <= m)

        update(p, delta, lhs); else

        update(p, delta, rhs);

    pushUp(rt); } int query(int beg, int end, int l, int r, int rt) { if (beg <= l && r <= end) return seg[rt]; int m = (l + r) >> 1; int ret = 0; if (beg <= m)

        ret = query(beg, end, lhs); if (end > m)

        ret = max(ret, query(beg, end, rhs)); return ret; } int main() { int n, m; while (scanf("%d %d", &n, &m) != EOF) {

        build(1, n, 1); while (m--) { char op[16]; int a, b;

            scanf("%s", op);

            scanf("%d %d", &a, &b); if (op[0] == 'Q')

                printf("%d\n", query(a, b, 1, n, 1)); else if (op[0] == 'U')

                update(a, b, 1, n, 1); } } return 0; }