201912-3 化学方程式

输入输出样例

样例1

输入

11
H2+O2=H2O
2H2+O2=2H2O
H2+Cl2=2NaCl
H2+Cl2=2HCl
CH4+2O2=CO2+2H2O
CaCl2+2AgNO3=Ca(NO3)2+2AgCl
3Ba(OH)2+2H3PO4=6H2O+Ba3(PO4)2
3Ba(OH)2+2H3PO4=Ba3(PO4)2+6H2O
4Zn+10HNO3=4Zn(NO3)2+NH4NO3+3H2O
4Au+8NaCN+2H2O+O2=4Na(Au(CN)2)+4NaOH
Cu+As=Cs+Au

输出

N
Y
N
Y
Y
Y
Y
Y
Y
Y
N

题解一

用Map来存储化学元素及其次数。难点在于嵌套括号的处理。100分。
参考：https://blog.csdn.net/qq_18287147/article/details/106981698?utm_medium=distribute.pc_relevant_download.none-task-blog-blogcommendfrombaidu-1.nonecase&depth_1-utm_source=distribute.pc_relevant_download.none-task-blog-blogcommendfrombaidu-1.nonecas

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;
public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(reader.readLine());
        for (int i = 0; i < n; ++i) {
            String raw = reader.readLine();
            String[] strs = raw.split("=");
            String left = strs[0];
            String right = strs[1];
            Map<String, Integer> mapA = handle(left);
            Map<String, Integer> mapB = handle(right);
//            System.out.println(mapA);
//            System.out.println(mapB);
//            System.out.println(mapA.equals(mapB));
            if (mapA.equals(mapB)){
                System.out.println("Y");
            }else {
                System.out.println("N");
            }
        }
    }
    private static Map<String, Integer> handle(String s) {
        Map<String, Integer> ans = new HashMap<>();
        for (String str : s.split("\\+")) {
            // System.out.println(str);
            int coef = 0;
            int i;
            for (i = 0; i < str.length(); ++i) {
                char ch = str.charAt(i);
                if (isDigit(ch)) {
                    coef = coef * 10 + ch - 48;
                } else {
                    break;
                }
            }
            handlePart(ans, str, i, str.length() - 1, Math.max(1, coef));
        }
        return ans;
    }
    private static void handlePart(Map<String, Integer> map, String s, int left, int right, int coef) {
        int i = left;
        while (i <= right) {
            if (s.charAt(i) == '(') { // 找到与这个左括号对应的右括号, 递归解析
                int depth = 1;
                int index;
                for (index = i + 1, depth = 1; depth > 0; ++index) {
                    if (s.charAt(index) == '(') {
                        ++depth;
                    } else if (s.charAt(index) == ')') {
                        --depth;
                    }
                }
                // 右括号左侧一位
                int r = index - 2;
                // 角标倍数
                int x = 0;
                while ((index <= right) && (isDigit(s.charAt(index)))) {
                    x = x * 10 + s.charAt(index) - 48;
                    ++index;
                }
                handlePart(map, s, i + 1, r, Math.max(coef, coef * x));
                i = index;
            } else if (s.charAt(i) == ')') {
                ++i;
            } else { // 化学元素首大写字母
                StringBuilder sBuilder = new StringBuilder();
                sBuilder.append(s.charAt(i));
                ++i;
                while ((i <= right) && (isLowerCase(s.charAt(i)))) {
                    sBuilder.append(s.charAt(i));
                    ++i;
                }
                // 元素符号
                String element = sBuilder.toString();
                // 角标倍数
                int x = 0;
                while ((i <= right) && (isDigit(s.charAt(i)))) {
                    x = x * 10 + s.charAt(i) - 48;
                    ++i;
                }
                map.put(element, (int) map.getOrDefault(element, 0) + Math.max(coef, x * coef));
            }
        }
    }
    private static boolean isDigit(char ch) {
        return (ch >= '0') && (ch <= '9');
    }
    private static boolean isLowerCase(char ch) {
        return (ch >= 'a') && (ch <= 'z');
    }
}