整数翻转（C++实现）

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#include <iostream>
using namespace std;

class Solution {
public:
    int reverse(int x) {
        int f = x<0 ? -1 : 1;
        x = abs(x);
        int d = digit(x);
        for(int i = 1; i <= d/2; i++) {
            swap(x, i, d-i+1);
        }
        return x*f;
    }
    
    int digit(int x) {
        int d = 0;
        while(x > 0) {
            x = x / 10;
            d++;
        }
        return d;
    }
    
    void swap(int &x, int i, int j) {
        int ei = vai(x, i);
        int ej = set_val(x, j, ei);
        set_val(x, i, ej);
    }
    
    int set_val(int &x, int i, int e) {
        assert(i >= 1);
        int dt = pow(10, i);
        int t = x % dt;
        if(i-1 <= 0) {
            x = x - t + e;
            return t;
        }
        dt /= 10;
        int ei = (t - x % dt) / dt;
        x += (e - ei) * dt;
        return ei;
    }
    
    // i start from 1
    int vai(int x, int i) {
        assert(i >= 1);
        int e = pow(10, i);
        int t = x % e;
        if (i-1 <= 0) return t;
        e = pow(10, i-1);
        t = (t - x % e) / e;
        return t;
    }
};


int main() {
    
    Solution *s = new Solution;
    
    int i = 12304;
    cout<<i<<endl;
    int r = s->reverse(i);
    cout<<r<<endl;
    
    return 0;
}

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