UVA 1362 - Exploring Pyramids（计数问题+区间DP）

#include <stdio.h>
#include <string.h>

const int N = 305;
const int MOD = 1000000000;
char str[N];
int n;
long long f[N][N];

int main() {
	while (~scanf("%s", str)) {
		memset(f, 0, sizeof(f));
		n = strlen(str);
		for (int len = 0; len < n; len += 2) {
			for (int l = 0; l + len < n; l++) {
				int r = l + len;
				if (l == r) f[l][r] = 1;
				for (int k = l + 2; k <= r; k+= 2) {
					if (str[l] == str[k] && str[k] == str[r]) {
						f[l][r] = (f[l][r] + f[l + 1][k - 1] * f[k][r]) % MOD;
					}
				}
			}
		}
		printf("%lld\n", f[0][n - 1]);
	}
	return 0;
}