代码实现：

方法一：遍历——超时

int maxPointsInsideSquare(int **points, int pointsSize, int *pointsColSize, char *s) {
    int a = 0;
    int flag = 1;
    int num, pre_num = 0;
    while (flag) {
        num = pre_num;
        pre_num = 0;
        int hash[26] = {0};
        for (int i = 0; i < pointsSize; i++) {
            if (abs(points[i][0]) <= a && abs(points[i][1]) <= a) {
                if (hash[s[i] - 'a']) {
                    flag = 0;
                    break;
                }
                pre_num++;
                hash[s[i] - 'a']++;
            }
        }
        if (pre_num == pointsSize) {
            num = pre_num;
            break;
        }
        if (flag) {
            a++;
        }
    }
    return num;
}

方法二：二分法

int func(int mid, int n, int **points, char *s) {
    int ret = 0;
    bool vis[26] = {0};
    for (int i = 0; i < n; i++) {
        if (abs(points[i][0]) <= mid && abs(points[i][1]) <= mid) {
            int c = s[i] - 'a';
            if (vis[c]) {
                return -1;
            }
            ret++;
            vis[c] = true;
        }
    }
    return ret;
}
int maxPointsInsideSquare(int **points, int pointsSize, int *pointsColSize, char *s) {
    int n = pointsSize;
    int head = 0, tail = 1e9;
    while (head < tail) {
        int mid = (head + tail) / 2;
        if (func(mid, n, points, s) >= 0) {
            head = mid + 1;
        } else {
            tail = mid;
        }
    }
    return func(head - 1, n, points, s);
}