RMQ_ST表

int STMax[maxn][];
int STMin[maxn][];
int pwr[];
void init(int n)
{
    int i, j;
    pwr[]  = ;
    for (i=; i<; ++i) pwr[i] = pwr[i-] << ;
    for (j=; pwr[j]<=n; ++j)
        for (i=; i+pwr[j]-<=n; ++i) {
            STMax[i][j] = max(STMax[i][j-], STMax[i+pwr[j-]][j-]);
            STMin[i][j] = min(STMin[i][j-], STMin[i+pwr[j-]][j-]);
        }
}

int query(int left, int right) {
    int x = int(log(double(right-left+)) / log(2.0));
    return max(STMax[left][x], STMax[right-pwr[x]+][x]) - min(STMin[left][x], STMin[right-pwr[x]+][x]);
}

附上别人讲解的博客   https://www.cnblogs.com/YSFAC/p/7189571.html

https://blog.csdn.net/jerry_wang119/article/details/79312519