整数二分

将区间分为 [l,mid] , [mid+1, r] (左边界)

int bsearch( int l, int r ) {
    while ( l < r ) {
        int mid = l + r >> 1;
        if ( check(mid)) r = mid;
        else l = mid+1;
    }
    return l;
}

将区间分为 [l, mid-1], [mid, r] (右边界)

int bsearch( int l, int r ) { 

  while ( l < r ) {
    int mid = l + r + 1 >> 1;
    if ( check(mid)) l = mid;
    else r = mid - 1;
  }
  return l;
}

浮点数二分

const double eps = 1e-8;
double bsearch( double l, double r ) {
    while ( r - l > eps) {
        double mid = ( l + r ) / 2;
        if ( check(mid)) r = mid;
        else l = mid;
    }
    return l;
}

算法第四版实现：

int bsearch( int l, int r ) {
    while( l < r ) {
        int mid = l + ( r - l ) / 2;
        if( check(mid)) r = mid - 1;
        else l = mid + 1;
    }
    return l;
}