[POJ 2774] Long Long Message 【后缀数组】

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;

const int MaxL = 200000 + 15;

int n, l1, l2, Ans;
int A[MaxL], Rank[MaxL], Height[MaxL], SA[MaxL];
int VA[MaxL], VB[MaxL], VC[MaxL], Sum[MaxL];

char S1[MaxL], S2[MaxL];

inline bool Cmp(int *a, int x, int y, int l) {
	return (a[x] == a[y]) && (a[x + l] == a[y + l]);
}

void DA(int *A, int n, int m) {
	int *x, *y, *t;
	x = VA; y = VB;
	for (int i = 1; i <= m; ++i) Sum[i] = 0;
	for (int i = 1; i <= n; ++i) ++Sum[x[i] = A[i]];
	for (int i = 2; i <= m; ++i) Sum[i] += Sum[i - 1];
	for (int i = n; i >= 1; --i) SA[Sum[x[i]]--] = i;
	int p, q;
	p = 0;
	for (int j = 1; p < n; j <<= 1, m = p) {
		q = 0;
		for (int i = n - j + 1; i <= n; ++i) y[++q] = i;
		for (int i = 1; i <= n; ++i) {
			if (SA[i] <= j) continue;
			y[++q] = SA[i] - j;
		}
		for (int i = 1; i <= n; ++i) VC[i] = x[y[i]];
		for (int i = 1; i <= m; ++i) Sum[i] = 0;
		for (int i = 1; i <= n; ++i) ++Sum[VC[i]];
		for (int i = 2; i <= m; ++i) Sum[i] += Sum[i - 1];
		for (int i = n; i >= 1; --i) SA[Sum[VC[i]]--] = y[i];
		t = x; x = y; y = t;
		x[SA[1]] = 1; p = 1;
		for (int i = 2; i <= n; ++i) 
			x[SA[i]] = Cmp(y, SA[i], SA[i - 1], j) ? p : ++p;
	}
	for (int i = 1; i <= n; ++i) Rank[SA[i]] = i;
	
	//GetHeight
	int h, o;
	h = 0;
	for (int i = 1; i <= n; ++i) {
		if (Rank[i] == 1) continue;
		o = SA[Rank[i] - 1];
		while (A[i + h] == A[o + h]) ++h;
		Height[Rank[i]] = h;
		if (h > 0) --h;
	} 
}

int main() 
{
	scanf("%s%s", S1 + 1, S2 + 1);
	l1 = strlen(S1 + 1);
	l2 = strlen(S2 + 1);
	for (int i = 1; i <= l1; ++i) 
		A[i] = S1[i] - ‘a‘ + 1;
	A[l1 + 1] = 27;
	for (int i = 1; i <= l2; ++i) 
		A[l1 + 1 + i] = S2[i] - ‘a‘ + 1;
	A[l1 + 1 + l2 + 1] = 28;
	n = l1 + 1 + l2 + 1;	
	DA(A, n, 28);	
	Ans = 0;
	for (int i = 2; i <= n - 1; ++i) {
		if (Height[i] > Ans) {
			if (SA[i] <= l1 && SA[i - 1] > l1 + 1) Ans = Height[i];
			if (SA[i] > l1 + 1 && SA[i - 1] <= l1) Ans = Height[i];
		}
	}
	printf("%d\n", Ans);
	return 0;
}