每日一题 - 240118 - P1981 [NOIP2013 普及组] 表达式求值

• P1981 [NOIP2013 普及组] 表达式求值

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• TAG - $芝士水题、算法-【STL-vector、模拟】、思维-【类栈】$
• 时间复杂度 - $O(N)$

//
#include 
using namespace std;
// #define int long long

const int MOD = 10000;
vector<int> v_num;
vector<char> v_op;
string s;

int f(int x, int y, bool isint) {   // 递归会WA？不理解捏
    if (isint) {
        int ans = 0;
        for (int i = x; i <= y; i++) {
            ans = ((ans << 3) + (ans << 1) + (s[i] - '0')) % MOD;
        }
        return ans;
    }

    for (int i = x; i <= y; i++) {
        if (s[i] == '*') {
            return (f(x, i - 1, 1) * f(i + 1, y, 0)) % MOD;
        } else if (s[i] == '+') {
            return (f(x, i - 1, 1) + f(i + 1, y, 0)) % MOD;
        }
    }
    return f(x, y, 1);
}

void solve() {
    cin >> s;

    for (int i = 0; i < s.size(); i++) {
        if (isdigit(s[i])) {
            int tt = 0;
            while (isdigit(s[i])) tt = ((tt << 3) + (tt << 1) + (s[i] - '0')) % MOD, i++;
            v_num.push_back(tt);

            if (s[i] == '*' || s[i] == '+') v_op.push_back(s[i]);
        }
    }

    int ans = 0, tt = v_num[0];
    for (int i = 0; i < v_op.size(); i++) {
        if (v_op[i] == '+') {
            ans = (ans + tt) % MOD;
            tt = v_num[i + 1];
        } else if (v_op[i] == '*') {
            tt = tt * v_num[i + 1] % MOD;
        }
    }
    ans = (ans + tt) % MOD;
    printf("%d\n", ans);

    // printf("%d\n", f(0, s.size() - 1, 0));
}

signed main() {
    int t = 1;
    // scanf("%d", &t);
    while (t--) solve();

    return 0;
}

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实现细节

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参考示意图

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参考链接

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作者 | 乐意奥AI