sort函数比较cmp写法

hihocoder1566http://hihocoder.com/problemset/problem/1566

一直WA因为cmp的写法写错了，未能正确实现排序功能。

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cstdlib>
#include<string>
#include<cmath>
#include<vector>
#include<stack>
#include<iterator>
#include<queue>
#include<cctype>
#include<map>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
#define IO ios::sync_with_stdio(false);cin.tie(0);
#define INF 0x3f3f3f3f
#define MAXN 100010
const int MOD=1e9+7;
typedef long long ll;
using namespace std;
int t;
typedef struct {
    char s1[110], s2[110];
    int sum;
}Node;
Node node[100010];
map<char, int> mp;
int cal(const char s[])
{
    int len = strlen(s), ans=0, last=mp[s[len-1]];
    for(int i = len-2; i >= 0; i--){
        if(last-mp[s[i]] > 0){
            last -= mp[s[i]];
        }
        else{
            ans += last;
            last = mp[s[i]];
        }
    }
    ans += last;
    return ans;
}
bool cmp(const Node a, const Node b)
{
    if(strcmp(a.s1, b.s1) != 0) return strcmp(a.s1, b.s1)<0;
    else{
        return a.sum < b.sum;
    }
}
int main()
{
    IO;
    mp['I']=1;mp['V']=5;mp['X']=10;mp['L']=50;mp['C']=100;mp['D']=500;mp['M']=1000;
    cin >> t;
    for(int i = 0; i < t; i++){
        cin >> node[i].s1 >> node[i].s2;
        node[i].sum = cal(node[i].s2);
        //cout << cal(node[i].s2) << endl;
    } 
    sort(node, node+t, cmp);
    for(int i = 0; i < t; i++){
        cout << node[i].s1 << " " << node[i].s2 << endl;
    }
    return 0;
}