题目链接：uva 261 - The Window Property

题目大意：给定给一个字符串，枚举子串长度k（len≥k≥1），要求在任意k时，有不超过k+1个不同的子串，如果有的话则输出NO，并且输出最早发现不满足的位置。

解题思路：后缀数组，处理出height数组，对于每个k，遍历height数组，碰到小于k的则分段，将整个height分成若干段，即为有多少种长度为k的不同前缀，需要注意的是要跳过前缀长度不足k的。

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

using namespace std;
const int maxn = 10005;

struct Suffix_Arr {
    char s[maxn];
    int n;
    int SA[maxn], height[maxn], rank[maxn];
    int tmp_one[maxn], tmp_two[maxn], c[maxn];

    bool input ();
    void build_suffix(int m);
    void get_height();
    int check(int k);
}fuck;

int main () {
    while (fuck.input()) {
        fuck.build_suffix(256);
        fuck.get_height();

        int ans = maxn;
        for (int i = 1; i <= fuck.n; i++)
            ans = min(ans, fuck.check(i));

        if (ans == maxn)
            printf("YES\n");
        else
            printf("NO:%d\n", ans + 1);
    }
    return 0;
}

bool Suffix_Arr::input () {
    if (!gets(s))
        return false;
    memset(height, 0, sizeof(height));
    n = strlen(s) + 1;
    return true;
}

int Suffix_Arr::check(int k) {
    int ret = 0;

    memset(c, -1, sizeof(c));

    for (int i = 1; i < n; i++) {

        if (height[i] < k)
            ret++;

        if (SA[i] > n - k - 1)
            continue;

        c[SA[i]] = ret;
    }

    /*
    for (int i = 1; i < n; i++)
        printf("%d", height[i]);
    printf("\n");

    for (int i = 1; i < n; i++)
        printf("%d", SA[i]);
    printf("\n");

    for (int i = 0; i < n; i++)
        printf("%d", c[i]);
    printf("\n");
    */

    set<int> g;
    ret = 0;
    for (int i = 0; i < n; i++) {
        if (c[i] == -1)
            continue;

        if (g.find(c[i]) == g.end()) {
            ret++;
            g.insert(c[i]);
        }

        if (ret > k + 1) {
    //        printf("%d %d!\n", k, i);
            return i + k - 1;
        }
    }
    return maxn;
}

void Suffix_Arr::get_height() {
    for (int i = 0; i < n; i++)
        rank[SA[i]] = i;

    int mv = 0;
    for (int i = 0; i < n; i++) {
        if (mv)
            mv--;

        if (rank[i] == 0) {
            height[rank[i]] = 0;
            continue;
        }

        int j = SA[rank[i]-1];
        while (s[i+mv] == s[j+mv])
            mv++;
        height[rank[i]] = mv;
    }
}

void Suffix_Arr::build_suffix(int m) {
    int *x = tmp_one, *y = tmp_two;

    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 mv = 0;
        for (int i = n - k; i < n; i++) y[mv++] = i;
        for (int i = 0; i < n; i++) if (SA[i] >= k)
            y[mv++] = 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);
        mv = 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] ? mv - 1 : mv++);

        if (mv >= n)
            break;
        m = mv;
    }
}

uva 261 - The Window Property(后缀数组)