hihoCoder#1077 RMQ问题再临-线段树

原题地址

终于做到线段树的题了，因为建树、更新、查询都是递归操作，所以其实挺好写的。

用数组存的树，记得MAX_NODE开成两倍叶节点数大小，否则RE啊。。不要问我是怎么知道的。

代码：

#include <iostream>
#include <climits>
using namespace std;

#define MAX_NODE 2000008

int N, Q;

struct SegmentTree {
  int left[MAX_NODE];
  int right[MAX_NODE];
  int begin[MAX_NODE];
  int end[MAX_NODE];
  int value[MAX_NODE];
  int root;
  int size;

  void init() {
    size = 1;
    left[0] = right[0] = root = 0;
    value[0] = INT_MAX;
  }

  int insert(int v) {
    value[size] = v;
    size++;
    return size - 1;
  }

  int _build(int l, int r) {
    if (l > r)
      return 0;
    if (l == r) {
      left[l] = right[l] = 0;
      begin[l] = end[l] = l;
      return l;
    }

    int lc = _build(l, (l + r) / 2);
    int rc = _build((l + r) / 2 + 1, r);
    int me = insert(-1);
    left[me] = lc;
    right[me] = rc;
    begin[me] = l;
    end[me] = r;
    value[me] = min(value[lc], value[rc]);

    return me;
  }

  void build() {
    root = _build(1, size - 1);
  }

  int _query(int n, int l, int r) {
    if (begin[n] == l && end[n] == r)
      return value[n];
    int medium = (begin[n] + end[n]) / 2;
    if (r <= medium)
      return _query(left[n], l, r);
    if (l > medium)
      return _query(right[n], l, r);
    return min(_query(left[n], l, medium), _query(right[n], medium + 1, r));
  }

  int query(int l, int r) {
    return _query(root, l, r);
  }

  void _update(int n, int p, int v) {
    if (begin[n] == p && end[n] == p) {
      value[p] = v;
      return;
    }
    int medium = (begin[n] + end[n]) / 2;
    if (p <= medium)
      _update(left[n], p, v);
    if (p > medium)
      _update(right[n], p, v);
    value[n] = min(value[left[n]], value[right[n]]);
  }

  void update(int p, int v) {
    _update(root, p, v);
  }
} st;

int main() {
  st.init();

  scanf("%d", &N);
  for (int i = 0; i < N; i++) {
    int v;
    scanf("%d", &v);
    st.insert(v);
  }

  st.build();

  scanf("%d", &Q);
  while (Q--) {
    int t, a, b;
    scanf("%d%d%d", &t, &a, &b);
    if (t)
      st.update(a, b);
    else
      printf("%d
", st.query(a, b));
  }

  return 0;
}