HDU 2151 Worm

#include <bits/stdc++.h>
using namespace std;

int dp[101][101];

int main() {
	int n, m, p, t;
	while(~scanf("%d%d%d%d", &n, &p, &m, &t)) {
		memset(dp, 0, sizeof(dp));
		dp[0][p] = 1;
		for(int i = 1; i <= m; i ++) {
			for(int j = 1; j <= n; j ++) {
				if(dp[i - 1][j - 1] != 0 || dp[i - 1][j + 1] != 0)
					dp[i][j] = dp[i - 1][j - 1] + dp[i - 1][j + 1];
			}
		}
		printf("%d\n", dp[m][t]);
	}
	return 0;
}