Leetcode-5207 Get Equal Substrings Within Budget(尽可能使字符串相等)

typedef long long ll;
#define _for(i,a,b) for(int i = (a);i < b;i ++)
#define _rep(i,a,b) for(int i = (a);i > b;i --)
#define INF 0x3f3f3f3f
#define pb push_back
#define maxn 10000

class Solution
{
    public:
        vector<int> d;
        int equalSubstring(string s, string t, int maxCost)
        {
            int ans = 0;
            _for(i,0,s.size())
            {
                if(s[i]>t[i])
                    d.pb(s[i]-t[i]);
                else
                    d.pb(t[i]-s[i]);
            }
            int st = 0,ed = 0;
            int sum = 0;
            while(ed < d.size() && st<=ed)
            {
                sum += d[ed];
                if(sum <= maxCost)
                {
                    ans = max(ans,ed-st+1);
                    ed ++;
                }
                else
                {
                    sum -= d[st];
                    st ++;
                    ed ++;
                }
            }
            return ans;
        }
};