CCF-CSP题解 201912-3 化学方程式

判断化学方程式是否配平。
字符串处理。
有点编译原理递归下降法的感觉。
考场源码，比较粗糙。
// INFO BEGIN

//

// User = 201911513451(陶杨)

// Group = C/C++

// Problem = 化学方程式

// Language = CPP11

// SubmitTime = 2019-12-15 16:20:32

//

// INFO END

#include <cstdio>

#include <cstring>

using namespace std;

char str[1005];

int nums[27][27];

void elementSingle(int l, int r, int left, int coef, int coef2) {

    if (l > r) return;

    int e1, e2 = 0;

    e1 = str[l] - 'A' + 1;  // [1,26]

    if (l < r && !(str[l + 1] >= '0' && str[l + 1] <= '9')) e2 = str[l + 1] - 'a' + 1;

    int mid = l + 1;

    if (e2 != 0) ++mid;

    int co = 0;

    while (mid <= r) co = co * 10 + str[mid++] - '0';

    if (co == 0) co = 1;

    nums[e1][e2] += left * coef * coef2 * co;

}

void element(int l, int r, int left, int coef, int coef2) {

    if (l > r) return;

    // printf("%d %d %d ", left, coef, coef2);

    // for (int i = l; i <= r; ++i) printf("%c", str[i]); printf("\n");

    int mid = l + 1;

    for (; mid <= r && !(str[mid] >= 'A' && str[mid] <= 'Z'); ++mid);

    if (mid <= r) {

        elementSingle(l, mid - 1, left, coef, coef2);

        element(mid, r, left, coef, coef2);

    } else elementSingle(l, r, left, coef, coef2);

}

void formula(int l, int r, int left, int coef, int coef2) {

    if (l > r) return;

    int lb = -1, rb = -1, lmore = 0;

    for (int i = l; i <= r; ++i) {

        if (str[i] == '(') {

            ++lmore;

            if (lb == -1) lb = i;

        }

        if (str[i] == ')') {

            --lmore;

            if (lmore == 0 && rb == -1) rb = i;

        }

        if (rb != -1) break;

    }

    if (rb == -1) element(l, r, left, coef, coef2); else {

        int co = 0, mid = rb + 1;

        for (; mid <= r && str[mid] >= '0' && str[mid] <= '9'; ++mid) co = co * 10 + str[mid] - '0';

        if (co == 0) co = 1;

        element(l, lb - 1, left, coef, coef2);

        formula(lb + 1, rb - 1, left, coef, coef2 * co);

        formula(mid, r, left, coef, coef2);

    }

}

void exprSingle(int l, int r, int left) {

    if (l > r) return;

    int coef = 0, mid = l;

    for (; mid <= r && str[mid] >= '0' && str[mid] <= '9'; ++mid) coef = coef * 10 + str[mid] - '0';

    if (coef == 0) coef = 1;

    formula(mid, r, left, coef, 1);

}

void expr(int l, int r, int left) {

    if (l > r) return;

    int mid = l;

    for (; mid <= r && str[mid] != '+'; ++mid);

    if (mid <= r) {

        exprSingle(l, mid - 1, left);

        expr(mid + 1, r, left);

    } else exprSingle(l, r, left);

}

// [l,r]

void equation(int l, int r) {

    if (l > r) return;

    int mid = l;

    for (; str[mid] != '='; ++mid);

    expr(l, mid - 1, 1);

    expr(mid + 1, r, -1);

}

int main() {

    int n;

    scanf("%d", &n);

    for (int _ = 0; _ < n; ++_) {

        scanf("%s", str);

        memset(nums, 0, sizeof(nums));

        equation(0, strlen(str) - 1);

        bool flag = true;

        for (int i = 1; i <= 26; ++i) {

            for (int j = 0; j <= 26; ++j) {

                if (nums[i][j] != 0)

                    flag = false;

            }

        }

        if (flag) printf("Y\n");

        else printf("N\n");

    }

    return 0;

}
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CCF-CSP题解 201912-3 化学方程式

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