Paint House I lc原题 需bug free

public int minCost(int[][] matrix) {
if(matrix==null||matrix.length==0)
return 0;
int m = matrix.length-1;
for(int i=1; i<matrix.length; i++){
matrix[i][0] += Math.min(matrix[i-1][1], matrix[i-1][2]);
matrix[i][1] += Math.min(matrix[i-1][0], matrix[i-1][2]);
matrix[i][2] += Math.min(matrix[i-1][0], matrix[i-1][1]);
}
return Math.min(Math.min(matrix[m][0], matrix[m][1]), matrix[m][2]);
}