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  • poj3264RMQ

    区间最值。学了下 st算法,o(1)的查询,这个要比线段树犀利。而且线段树的log(n)前面的常数也比较大。

    #include<iostream>
    #include<cstdio>
    #include<cstring>
    
    using namespace std;
    
    int n, q;
    const int maxn = 111111;
    int dp[maxn][20];
    int dp1[maxn][20];
    int a[maxn];
    void gao()
    {
        for (int i = 0; i < n; i++)
            dp[i][0] = a[i];
        for (int j = 1; (1 << j) <= n; j++){
            for (int i = 0; i + (1 << j) - 1 < n; i++){
                dp[i][j] = min(dp[i][j - 1], dp[i + (1 << (j-1))][j - 1]);
            }
        }
    }
    
    int ask(int l, int r)
    {
        int k = 0;
        while ((1 << (k + 1)) <= r - l + 1) k++;
        return min(dp[l][k], dp[r-(1<<k)+1][k]);
    }
    
    void gao1()
    {
        memset(dp1,0,sizeof(dp1));
        for (int i = 0; i < n; i++)
            dp1[i][0] = a[i];
        for (int j = 1; (1 << j) <= n; j++){
            for (int i = 0; i + (1 << j) - 1 < n; i++){
                dp1[i][j] = max(dp1[i][j - 1], dp1[i + (1 << (j-1))][j - 1]);
            }
        }
    }
    
    int ask1(int l, int r)
    {
        int k = 0;
        while ((1 << (k + 1)) <= r - l + 1) k++;
        return max(dp1[l][k], dp1[r + 1 - (1 << k)][k]);
    }
    
    int main()
    {
        int l, r;
        while (cin >> n >> q){
            for (int i = 0; i < n; i++)
                scanf("%d",&a[i]);
            gao(); gao1();
            for (int i = 0; i < q; i++){
                scanf("%d%d",&l,&r);
                l--;r--;
                printf("%d
    ",ask1(l,r)- ask(l,r));
            }
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/yigexigua/p/4018596.html
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