RMQ 总结

#include <cstdio>
#include <algorithm>
#include <cmath>

using namespace std;
const int maxn = 1000 + 100;
int a[1000 + 100], n;
int dp[1000 + 100][30];   //以i开始长度为2^j的最小值

int main() {
    scanf("%d", &n);
    for(int i=0; i<n; i++) scanf("%d", &a[i]);
    for(int i=0; i<n; i++) dp[i][0] = a[i];        //初始化值
    for(int j=1; j<=n; j*=2)                       //计算区间最小值
    for(int i=0; i<n; i++) if(i+(1<<(j-1))<n){
        dp[i][j] = min(dp[i][j-1], dp[i+(1<<(j-1))][j-1]);
    }

    int q;
    scanf("%d", &q);                    //q个查询
    for(int i=0; i<q; i++) {
        int l, r;
        scanf("%d%d", &l, &r);
        int m = log(r-l+1)/log(2);
        int ans = min(dp[l][m], dp[r-(1<<(m))+1][m]);
        printf("%d\n", ans);
    }
    return 0;
}

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;
const int maxn = 200000 + 100;
int n, m;
int a[maxn];

struct Segment{
    int l, r;
    int num;
}seg[3*maxn];

void build(int rt, int l, int r){    //建树
    seg[rt].l = l; seg[rt].r = r;
    if(l == r){
        seg[rt].num = a[l];
    }else{
        int chl=2*rt, chr=2*rt+1;
        build(chl, l, (l+r)/2);
        build(chr, (l+r)/2+1, r);
        seg[rt].num = max(seg[2*rt].num, seg[2*rt+1].num);
    }
}

int query(int rt, int l, int r){     //查询l-r区间的最大值
    if(seg[rt].l==l && seg[rt].r==r){
        return seg[rt].num;
    }
    int mid = (seg[rt].l+seg[rt].r)/2;
    if(r<=mid)                      //l-r位于左区间
        return query(2*rt, l, r);
    else if(l>mid)                  //l-r位于右区间
        return query(2*rt+1, l, r);
    else {
        int v1 = query(2*rt, l, mid);
        int v2 = query(2*rt+1, mid+1, r);
        return max(v1, v2);
    }
}

void update(int rt, int i, int g){   //将同学i的成绩改为g
    if(seg[rt].l==i && seg[rt].r==i){
        seg[rt].num = g;
        return ;
    }
    int mid = (seg[rt].l+seg[rt].r)/2;
    if(i <= mid) update(2*rt, i, g);
    else update(2*rt+1, i, g);
    seg[rt].num = max(seg[2*rt].num, seg[2*rt+1].num);  //回溯时更新数组
}

int main() {
    while(scanf("%d%d", &n, &m) == 2){
        for(int i=1; i<=n; i++) scanf("%d", &a[i]);
        build(1, 1, n);
        char str[10]; int l, r;
        for(int i=0; i<m; i++){
            scanf("%s%d%d", str, &l, &r);
            if(str[0] == ‘Q‘){
                printf("%d\n", query(1, l, r));
            }else{
                update(1, l, r);
            }
        }
    }
    return 0;
}