public int minCost(int[][] costs) {

if (costs == null || costs.length == 0) return 0;

int N = costs.length;

int[][] dp = new int[N + 1][3];

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

dp[i][0] = Math.min(dp[i-1][1], dp[i-1][2]) + costs[i-1][0];

dp[i][1] = Math.min(dp[i-1][0], dp[i-1][2]) + costs[i-1][1];

dp[i][2] = Math.min(dp[i-1][0], dp[i-1][1]) + costs[i-1][2];

}

return Math.min(dp[N][0], Math.min(dp[N][1], dp[N][2]));

}

public int minCost2(int[][] costs) {

if (costs == null || costs.length == 0) return 0;

int N = costs.length;

int red = 0;

int blue = 0;

int green = 0;

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

int r = red;

int b = blue;

int g = green;

red = Math.min(b, g) + costs[i-1][0];

blue = Math.min(r, g) + costs[i-1][1];

green = Math.min(r, b) + costs[i-1][2];

}

return Math.min(red, Math.min(blue, green));

}