public NFADemo(String regexp) {
// use stack to keep track of the positions of '('and '|'
// issue : or的优先级最低
Stack<Integer> ops = new Stack<Integer>();
re = regexp.toCharArray();
M = re.length;
G = new Digraph(M + 1);
// 第一次遍历，确定层次，仅为作图用
int[] levels = new int[M]; // levels仅在 * 和 | 处非零
for (int i = 0; i < M; i++) {
int lp = i;
if (re[i] == '(' || re[i] == '|') ops.push(i);
else if (re[i] == ')') {
int or = ops.pop();
if (re[or] == '|') {
lp = ops.pop();
levels[or] = maxOfArr(levels, lp, i) + 1;
} else lp = or;
}
if (i < M - 1 && re[i + 1] == '*') levels[i + 1] = maxOfArr(levels, lp, i + 1) + 1;
}
int maxLevel = maxOfArr(levels, 0, M);
StdDraw.setCanvasSize(800, 800 * 2 * maxLevel / M);
StdDraw.setXscale(0, M);
StdDraw.setYscale(-maxLevel, maxLevel);
double r = 0.2;
for (int v = 0; v < G.V(); v++) {
if (v < M) {
StdDraw.circle((double) v, 0.0, r);
StdDraw.text((double) v, 0.0, (new Character(re[v]).toString()));
} else StdDraw.filledCircle((double) v, 0.0, r);
}
StdDraw.setPenColor(StdDraw.RED);
StdDraw.setPenRadius(0.005);
ops = new Stack<Integer>();
for (int i = 0; i < M; i++) {
int lp = i;
if (re[i] == '(' || re[i] == '|') ops.push(i);
else if (re[i] == ')') {
int or = ops.pop();
if (re[or] == '|') {
lp = ops.pop();
G.addEdge(lp, or + 1);
G.addEdge(or, i);
// connect (lp, or+1), (or, i)
double level = (double) levels[or];
StdDraw.line(or, r, or, level);
StdDraw.line(or, level, i, level);
StdDraw.arrow(i, level, i, r);
StdDraw.line(lp, -r, lp, -level);
StdDraw.line(lp, -level, or + 1, -level);
StdDraw.filledArrow(or + 1, -level, or + 1, -r);
} else lp = or; // 此时是'(', 在后面跟的是*时会用到
}
if (i < M - 1 && re[i + 1] == '*') {
// look ahead
G.addEdge(lp, i + 1);
G.addEdge(i + 1, lp);
// connect (lp, i+1), (i+1, lp)
double level = (double) levels[i + 1];
StdDraw.line(i + 1, r, i + 1, level);
StdDraw.line(i + 1, level, lp, level);
StdDraw.filledArrow(lp, level, lp, r);
StdDraw.line(lp, -r, lp, -level);
StdDraw.line(lp, -level, i + 1, -level);
StdDraw.filledArrow(i + 1, -level, i + 1, -r);
}
if (re[i] == '(' || re[i] == '*' || re[i] == ')') {
G.addEdge(i, i + 1);
StdDraw.filledArrow(i + r, 0.0, i + 1 - r, 0.0);
} else if (re[i] != '|') { // match transitions
StdDraw.setPenColor();
StdDraw.filledArrow(i + r, 0.0, i + 1 - r, 0.0);
StdDraw.setPenColor(StdDraw.RED);
}
}
}
