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package class08;
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import java.util.LinkedList;
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// 本题测试链接 : https://leetcode.com/problems/basic-calculator-iii/
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public class Code01_ExpressionCompute {
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public static int calculate(String str) {
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return f(str.toCharArray(), 0)[0];
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}
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// 请从str[i...]往下算，遇到字符串终止位置或者右括号，就停止
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// 返回两个值，长度为2的数组
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// 0) 负责的这一段的结果是多少
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// 1) 负责的这一段计算到了哪个位置
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public static int[] f(char[] str, int i) {
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LinkedList<String> queue = new LinkedList<String>();
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int cur = 0;
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int[] bra = null;
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// 从i出发，开始撸串
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while (i < str.length && str[i] != ')') {
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if (str[i] >= '0' && str[i] <= '9') {
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cur = cur * 10 + str[i++] - '0';
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} else if (str[i] != '(') { // 遇到的是运算符号
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addNum(queue, cur, str[i++]);
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cur = 0;
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} else { // 遇到左括号了
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bra = f(str, i + 1);
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cur = bra[0];
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i = bra[1] + 1;
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}
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}
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addNum(queue, cur, '+');
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return new int[] { getAns(queue), i };
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}
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public static void addNum(LinkedList<String> queue, int num, char op) {
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if (!queue.isEmpty() && (queue.peekLast().equals("*") || queue.peekLast().equals("/"))) {
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String top = queue.pollLast();
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int pre = Integer.valueOf(queue.pollLast());
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num = top.equals("*") ? (pre * num) : (pre / num);
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}
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queue.addLast(String.valueOf(num));
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queue.addLast(String.valueOf(op));
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}
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public static int getAns(LinkedList<String> queue) {
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int ans = Integer.valueOf(queue.pollFirst());
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while (queue.size() > 1) {
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String op = queue.pollFirst();
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int num = Integer.valueOf(queue.pollFirst());
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ans += op.equals("+") ? num : -num;
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}
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return ans;
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}
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}
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