【HDU 1754】 I Hate It

【题目链接】

           点击打开链接

【算法】

          树状数组的最值查询

          详见这篇文章 ： https://blog.csdn.net/u010598215/article/details/48206959

【代码】

           

#include<bits/stdc++.h>
using namespace std;
#define MAXN 200000

int i,N,M,x,y,b;
int a[MAXN+10];
char opt;

template <typename T> inline void read(T &x) {
      int f = 1; x = 0;
      char c = getchar();
      for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
      for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
      x *= f;
}

template <typename T> inline void write(T x) {
    if (x < 0) { putchar('-'); x = -x; }
    if (x > 9) write(x/10);
    putchar(x%10+'0');
}

template <typename T> inline void writeln(T x) {
    write(x);
    puts("");
}

struct BinaryIndexedTree {
      int bit[MAXN+10];
      inline int lowbit(int x) { return x & -x; }
      inline void clear() {
            int i;
          for (i = 1; i <= N; i++) bit[i] = 0;
      }
      inline void modify(int pos,int val) {
          int i,j,t;
          for (i = pos; i <= N; i += lowbit(i)) {
              bit[i] = a[i];
              t = lowbit(i);
              for (j = 1; j < t; j <<= 1) bit[i] = max(bit[i],bit[i-j]);
          }
        }
        inline int query(int l,int r) {
          int ret = 0;
          while (r >= l) {
              if (r - lowbit(r) < l) { 
                  ret = max(ret,a[r]);
                  r--;
                  continue;
              }
              while (r - lowbit(r) >= l) {
                  ret = max(ret,bit[r]);
                  r -= lowbit(r);
              }
          }
          return ret;
        }
} BIT;

int main() {
        
      while (scanf("%d%d",&N,&M) != EOF) {
          BIT.clear();
          for (i = 1; i <= N; i++) {
              read(a[i]);
              BIT.modify(i,a[i]);    
          }
          while (M--) {
              opt = getchar();
              if (opt == 'U')    {
                  read(x); read(b);
                  a[x] = b;
                  BIT.modify(x,b);
              } else {
                  read(x); read(y);
                  writeln(BIT.query(x,y));
              }
          }
      }
      
      return 0;
}