ST表-求RMQ(区间最值)问题。

Code:

#include<bits/stdc++.h>
using namespace std;
const int MAX = 2000;
int n, m, x, y;
int a[MAX + 5], lg[MAX + 5], maxn[MAX + 5][MAX + 5];
void solve(int *x) {
	for (int i = 1; i <= n; i++) {
		lg[i] = lg[i - 1];
		if (1 << lg[i - 1] + 1 == i) lg[i]++;
		//cout << "lg[" << i << "]:" << lg[i] << endl;
	}
	for (int j = 1; j <= lg[n]; j++)
	{
		for (int i = 1; i + (1 << j) - 1 <= n; i++)
		{
			maxn[i][j] = max(maxn[i][j - 1], maxn[i + 1 << (j - 1)][j - 1]);
		}
	}

}
int askm(int l, int r) {
	int k = lg[r - l + 1];
	return max(maxn[l][k], maxn[r - (1 << k) + 1][k]);
}
int main() {
	cin >> n >> m;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		maxn[i][0] = a[i];
	}
	solve(a);
	//for (int i = 1; i <= n; ++i)
	//{
	//	for (int j = 0; j <= n; ++j)
	//	{
	//		cout << "max[" << i << "][" << j << "]:" << maxn[i][j] << " ";
	//	}
	//	cout << endl;
	//}
		for (int i = 1; i <= m; i++) {
			cin >> x >> y;
			cout << askm(x, y) << endl;
		}
	return 0;
}

Analysis:

竖着读maxn数组：

 

Code2：

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
#include<cmath>
using namespace std;
int a[100001],f[100001][20];
inline int read(){
    int x=0,f=1;
    char c=getchar();
    for(;!isdigit(c);c=getchar())
        if(c=='-')
            f=-1;
    for(;isdigit(c);c=getchar())
        x=x*10+c-'0';
    return x*f;
}
void RMQ(int N){
    for(int j=1;j<=20;j++)    
        for(int i=1;i<=N;i++)
            if(i+(1<<j)-1<=N)
                f[i][j]=max(f[i][j-1],f[i+(1<<(j-1))][j-1]); 
}
int main(){
    int N=read(),M=read();
    for(int i=1;i<=N;i++) a[i]=read();
    for(int i=1;i<=N;i++) f[i][0]=a[i];
    RMQ(N); 
    while(M--){
        int i=read(),j=read();
         int k=(int)(log((double)(j-i+1))/log(2.0)); 
        printf("%d\n",max(f[i][k],f[j-(1<<k)+1][k]));
    }
    return 0;
}