查找给定的数字是否是完全平方？

Question

public boolean isPerfectSquare(int n) {
    int l=1, r=n;
    if(r==l) return true;
    return searchBinary(l, r, n);
}
public boolean searchBinary(int l, int r, int n){
    if(r>l){
        int mid=l+(r-l)/2;
      //  System.out.println(l + " " + r + " " + mid + " " +n);
        if(mid*mid == n) return true;
        else if(mid*mid>n) return searchBinary(l, mid-1, n);
        else return searchBinary(mid+1, r, n);
    }
    return false;
}

My code is failing for n=808201

I'm not getting why it's not working. This code looks Ok to me. Any suggestions?

Answer 1

Because mid * mid exceding int range.

for n=808201, you fail at mid = 300325, change to long value

public static boolean isPerfectSquare(int n) {
        int l=1, r=n;
        if(r==l) return true;
        return searchBinary(l, r, n);
    }
    public static boolean searchBinary(long l, long r, int n){
        if (l > r) {
            return false;
        }
        long mid=(r + l) >> 1;
        //  System.out.println(l + " " + r + " " + mid + " " +n);
        if(mid*mid == n) return true;
        else if(mid*mid>n) return searchBinary(l, mid-1, n);
        else return searchBinary(mid+1, r, n);
    }