POJ1743 Musical Theme

后缀数组典型题。

给定一个字符串，求最长重复子串，这两个子串不能重叠。

计算height数组，然后二分答案k，连续的height >= k的区间中sa相差最大的差若超过k，则符合条件。

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 20005;
int a[maxn], s[maxn];
int n, ans, sa[maxn], sx[maxn], sy[maxn], c[maxn];
int rank[maxn], height[maxn];

void build_sa(int m)
{
    int *x = sx, *y = sy;
    for (int i = 0; i < m; i++) c[i] = 0;
    for (int i = 0; i < n; i++) c[x[i] = s[i]]++;
    for (int i = 1; i < m; i++) c[i] += c[i-1];
    for (int i = n-1; i >= 0; i--) sa[--c[x[i]]] = i;
    for (int k = 1; k <= n; k <<= 1)
    {
        int p = 0;
        for (int i = n-k; i < n ; i++) y[p++] = i;
        for (int i = 0; i < n; i++) if (sa[i] >= k) y[p++] = sa[i] - k;
        for (int i = 0; i < m; i++) c[i] = 0;
        for (int i = 0; i < n; i++) c[x[y[i]]]++;
        for (int i = 1; i < m; i++) c[i] += c[i-1];
        for (int i = n-1; i >= 0; i--) sa[--c[x[y[i]]]] = y[i];
        swap(x, y);
        p = 1; x[sa[0]] = 0;
        for (int i = 1; i < n; i++)
            x[sa[i]] = (y[sa[i-1]]==y[sa[i]] && y[sa[i-1]+k]==y[sa[i]+k]) ? p-1 : p++;
        if (p >= n) break;
        m = p;
    }
}

void getHeight()
{
    int k = 0;
    for (int i = 0; i < n; i++) rank[sa[i]] = i;
    for (int i = 0; i < n; i++)
    {
        if (rank[i] <= 0) continue;
        if (k) k--;
        int j = sa[rank[i]-1];
        while (i+k<n && j+k<n && s[i+k] == s[j+k]) k++;
        height[rank[i]] = k;
    }
}

bool judge(int k)
{
    int go = 0, mx, mn;
    for (int i=1;i<n;i++)
    {
        if (height[i] >= k)
        {
            if (!go)
            {
                go = 1;
                mx = mn = sa[i-1];
            }
            mx = max(mx, sa[i]);
            mn = min(mn, sa[i]);
            if (mx - mn >= k) return 1;
        }
        else go = 0;
    }
    return 0;
}

int main()
{
    while (scanf("%d", &n) == 1 && n)
    {
        for (int i=0;i<n;i++) scanf("%d", &a[i]);
        for (int i=0;i<n-1;i++) s[i] = 90 + a[i+1] - a[i];
        s[n-1] = 0;
        build_sa(180);
        getHeight();
        int low = 0, high = n / 2, mid;
        while (low < high)
        {
            mid = (low + high) / 2;
            if (judge(mid)) low = mid + 1;
            else high = mid;
        }
        ans = high;
        if (ans < 5) puts("0");
        else printf("%d\n", ans);
    }
    return 0;
}