【CodeForces】779D - String Game（二分）

#include <cstdio>
#include <cstring>
#include <queue>
#include <cmath>
#include <stack>
#include <vector>
#include <algorithm>
using namespace std;
#define INF 0x3f3f3f3f
#define CLR(a,b) memset(a,b,sizeof(a))
#define PI acos(-1.0)
#define LL long long
char str1[200000+5],str2[200000+5];
int arr[200000+5];
int l1,l2;
bool check(int mid)
{
    int pos1 = 1,pos2 = 1;
    while (pos2 <= l2)
    {
        if (pos1 > l1)
            return false;
        if (arr[pos1] <= mid)
        {
            pos1++;
            continue;
        }
        if (str1[pos1] == str2[pos2])
        {
            pos1++;
            pos2++;
        }
        else
            pos1++;
    }
    return true;
}
int main()
{
    scanf ("%s %s",str1+1,str2+1);
    l1 = strlen(str1+1);
    l2 = strlen(str2+1);
    for (int i = 1 ; i <= l1 ; i++)
    {
        int t;
        scanf ("%d",&t);
        arr[t] = i;
    }
    int l = 0,r = l1-l2;
    while (r >= l)
    {
        int mid = (l + r) >> 1;
        if (check(mid))
            l = mid+1;
        else
            r = mid-1;
    }
    printf ("%d\n",r);
    return 0;
}